- 25 Jul, 2018 40 commits
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Kees Cook authored
commit 7bbf1373 upstream Adjust arch_prctl_get/set_spec_ctrl() to operate on tasks other than current. This is needed both for /proc/$pid/status queries and for seccomp (since thread-syncing can trigger seccomp in non-current threads). Signed-off-by:
Kees Cook <keescook@chromium.org> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
David Woodhouse <dwmw@amazon.co.uk> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by:
Srivatsa S. Bhat <srivatsa@csail.mit.edu> Reviewed-by:
Matt Helsley (VMware) <matt.helsley@gmail.com> Reviewed-by:
Alexey Makhalov <amakhalov@vmware.com> Reviewed-by:
Bo Gan <ganb@vmware.com> Signed-off-by:
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Thomas Gleixner authored
commit a73ec77e upstream Add prctl based control for Speculative Store Bypass mitigation and make it the default mitigation for Intel and AMD. Andi Kleen provided the following rationale (slightly redacted): There are multiple levels of impact of Speculative Store Bypass: 1) JITed sandbox. It cannot invoke system calls, but can do PRIME+PROBE and may have call interfaces to other code 2) Native code process. No protection inside the process at this level. 3) Kernel. 4) Between processes. The prctl tries to protect against case (1) doing attacks. If the untrusted code can do random system calls then control is already lost in a much worse way. So there needs to be system call protection in some way (using a JIT not allowing them or seccomp). Or rather if the process can subvert its environment somehow to do the prctl it can already execute arbitrary code, which is much worse than SSB. To put it differently, the point of the prctl is to not allow JITed code to read data it shouldn't read from its JITed sandbox. If it already has escaped its sandbox then it can already read everything it wants in its address space, and do much worse. The ability to control Speculative Store Bypass allows to enable the protection selectively without affecting overall system performance. Based on an initial patch from Tim Chen. Completely rewritten. Signed-off-by:
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by:
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Thomas Gleixner authored
commit 885f82bf upstream The Speculative Store Bypass vulnerability can be mitigated with the Reduced Data Speculation (RDS) feature. To allow finer grained control of this eventually expensive mitigation a per task mitigation control is required. Add a new TIF_RDS flag and put it into the group of TIF flags which are evaluated for mismatch in switch_to(). If these bits differ in the previous and the next task, then the slow path function __switch_to_xtra() is invoked. Implement the TIF_RDS dependent mitigation control in the slow path. If the prctl for controlling Speculative Store Bypass is disabled or no task uses the prctl then there is no overhead in the switch_to() fast path. Update the KVM related speculation control functions to take TID_RDS into account as well. Based on a patch from Tim Chen. Completely rewritten. Signed-off-by:
Ingo Molnar <mingo@kernel.org> Reviewed-by:
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Thomas Gleixner authored
commit 5a920155 upstream Provide and use a toggle helper instead of doing it with a branch. x86_64: arch/x86/kernel/process.o text data bss dec hex 3008 8577 16 11601 2d51 Before 2976 8577 16 11569 2d31 After i386: arch/x86/kernel/process.o text data bss dec hex 2925 8673 8 11606 2d56 Before 2893 8673 8 11574 2d36 After Signed-off-by:
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Kyle Huey authored
commit b9894a2f upstream The debug control MSR is "highly magical" as the blockstep bit can be cleared by hardware under not well documented circumstances. So a task switch relying on the bit set by the previous task (according to the previous tasks thread flags) can trip over this and not update the flag for the next task. To fix this its required to handle DEBUGCTLMSR_BTF when either the previous or the next or both tasks have the TIF_BLOCKSTEP flag set. While at it avoid branching within the TIF_BLOCKSTEP case and evaluating boot_cpu_data twice in kernels without CONFIG_X86_DEBUGCTLMSR. x86_64: arch/x86/kernel/process.o text data bss dec hex 3024 8577 16 11617 2d61 Before 3008 8577 16 11601 2d51 After i386: No change [ tglx: Made the shift value explicit, use a local variable to make the code readable and massaged changelog] Originally-by:
Kyle Huey <khuey@kylehuey.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Link: http://lkml.kernel.org/r/20170214081104.9244-3-khuey@kylehuey.comSigned-off-by:
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Kyle Huey authored
commit af8b3cd3 upstream Help the compiler to avoid reevaluating the thread flags for each checked bit by reordering the bit checks and providing an explicit xor for evaluation. With default defconfigs for each arch, x86_64: arch/x86/kernel/process.o text data bss dec hex 3056 8577 16 11649 2d81 Before 3024 8577 16 11617 2d61 After i386: arch/x86/kernel/process.o text data bss dec hex 2957 8673 8 11638 2d76 Before 2925 8673 8 11606 2d56 After Originally-by:
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Thomas Gleixner authored
commit b617cfc8 upstream Add two new prctls to control aspects of speculation related vulnerabilites and their mitigations to provide finer grained control over performance impacting mitigations. PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature which is selected with arg2 of prctl(2). The return value uses bit 0-2 with the following meaning: Bit Define Description 0 PR_SPEC_PRCTL Mitigation can be controlled per task by PR_SET_SPECULATION_CTRL 1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is disabled 2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is enabled If all bits are 0 the CPU is not affected by the speculation misfeature. If PR_SPEC_PRCTL is set, then the per task control of the mitigation is available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation misfeature will fail. PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which is selected by arg2 of prctl(2) per task. arg3 is used to hand in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE. The common return values are: EINVAL prctl is not implemented by the architecture or the unused prctl() arguments are not 0 ENODEV arg2 is selecting a not supported speculation misfeature PR_SET_SPECULATION_CTRL has these additional return values: ERANGE arg3 is incorrect, i.e. it's not either PR_SPEC_ENABLE or PR_SPEC_DISABLE ENXIO prctl control of the selected speculation misfeature is disabled The first supported controlable speculation misfeature is PR_SPEC_STORE_BYPASS. Add the define so this can be shared between architectures. Based on an initial patch from Tim Chen and mostly rewritten. Signed-off-by:
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Thomas Gleixner authored
commit 28a27752 upstream Having everything in nospec-branch.h creates a hell of dependencies when adding the prctl based switching mechanism. Move everything which is not required in nospec-branch.h to spec-ctrl.h and fix up the includes in the relevant files. Signed-off-by:
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David Woodhouse authored
commit 764f3c21 upstream AMD does not need the Speculative Store Bypass mitigation to be enabled. The parameters for this are already available and can be done via MSR C001_1020. Each family uses a different bit in that MSR for this. [ tglx: Expose the bit mask via a variable and move the actual MSR fiddling into the bugs code as that's the right thing to do and also required to prepare for dynamic enable/disable ] [ Srivatsa: Removed __ro_after_init for 4.4.y ] Suggested-by:
Borislav Petkov <bp@suse.de> Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 1115a859 upstream Intel and AMD SPEC_CTRL (0x48) MSR semantics may differ in the future (or in fact use different MSRs for the same functionality). As such a run-time mechanism is required to whitelist the appropriate MSR values. [ tglx: Made the variable __ro_after_init ] [ Srivatsa: Removed __ro_after_init for 4.4.y ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 77243971 upstream Intel CPUs expose methods to: - Detect whether RDS capability is available via CPUID.7.0.EDX[31], - The SPEC_CTRL MSR(0x48), bit 2 set to enable RDS. - MSR_IA32_ARCH_CAPABILITIES, Bit(4) no need to enable RRS. With that in mind if spec_store_bypass_disable=[auto,on] is selected set at boot-time the SPEC_CTRL MSR to enable RDS if the platform requires it. Note that this does not fix the KVM case where the SPEC_CTRL is exposed to guests which can muck with it, see patch titled : KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS. And for the firmware (IBRS to be set), see patch titled: x86/spectre_v2: Read SPEC_CTRL MSR during boot and re-use reserved bits [ tglx: Distangled it from the intel implementation and kept the call order ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 24f7fc83 upstream Contemporary high performance processors use a common industry-wide optimization known as "Speculative Store Bypass" in which loads from addresses to which a recent store has occurred may (speculatively) see an older value. Intel refers to this feature as "Memory Disambiguation" which is part of their "Smart Memory Access" capability. Memory Disambiguation can expose a cache side-channel attack against such speculatively read values. An attacker can create exploit code that allows them to read memory outside of a sandbox environment (for example, malicious JavaScript in a web page), or to perform more complex attacks against code running within the same privilege level, e.g. via the stack. As a first step to mitigate against such attacks, provide two boot command line control knobs: nospec_store_bypass_disable spec_store_bypass_disable=[off,auto,on] By default affected x86 processors will power on with Speculative Store Bypass enabled. Hence the provided kernel parameters are written from the point of view of whether to enable a mitigation or not. The parameters are as follows: - auto - Kernel detects whether your CPU model contains an implementation of Speculative Store Bypass and picks the most appropriate mitigation. - on - disable Speculative Store Bypass - off - enable Speculative Store Bypass [ tglx: Reordered the checks so that the whole evaluation is not done when the CPU does not support RDS ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 0cc5fa00 upstream Add the CPU feature bit CPUID.7.0.EDX[31] which indicates whether the CPU supports Reduced Data Speculation. [ tglx: Split it out from a later patch ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit c456442c upstream Add the sysfs file for the new vulerability. It does not do much except show the words 'Vulnerable' for recent x86 cores. Intel cores prior to family 6 are known not to be vulnerable, and so are some Atoms and some Xeon Phi. It assumes that older Cyrix, Centaur, etc. cores are immune. Signed-off-by:
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Piotr Luc authored
commit 0047f598 upstream Add CPUID of Knights Mill (KNM) processor to Intel family list. Signed-off-by:
Piotr Luc <piotr.luc@intel.com> Reviewed-by:
Dave Hansen <dave.hansen@intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20161012180520.30976-1-piotr.luc@intel.comSigned-off-by:
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Andy Shevchenko authored
commit f5fbf848 upstream Merrifield2 is actually Moorefield. Rename it accordingly and drop tail digit from Merrifield1. Signed-off-by:
Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20160906184254.94440-1-andriy.shevchenko@linux.intel.comSigned-off-by:
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Konrad Rzeszutek Wilk authored
commit 5cf68754 upstream A guest may modify the SPEC_CTRL MSR from the value used by the kernel. Since the kernel doesn't use IBRS, this means a value of zero is what is needed in the host. But the 336996-Speculative-Execution-Side-Channel-Mitigations.pdf refers to the other bits as reserved so the kernel should respect the boot time SPEC_CTRL value and use that. This allows to deal with future extensions to the SPEC_CTRL interface if any at all. Note: This uses wrmsrl() instead of native_wrmsl(). I does not make any difference as paravirt will over-write the callq *0xfff.. with the wrmsrl assembler code. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 1b86883c upstream The 336996-Speculative-Execution-Side-Channel-Mitigations.pdf refers to all the other bits as reserved. The Intel SDM glossary defines reserved as implementation specific - aka unknown. As such at bootup this must be taken it into account and proper masking for the bits in use applied. A copy of this document is available at https://bugzilla.kernel.org/show_bug.cgi?id=199511 [ tglx: Made x86_spec_ctrl_base __ro_after_init ] [ Srivatsa: Removed __ro_after_init for 4.4.y ] Suggested-by:
Jon Masters <jcm@redhat.com> Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit d1059518 upstream Those SysFS functions have a similar preamble, as such make common code to handle them. Suggested-by:
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Konrad Rzeszutek Wilk authored
commit 4a28bfe3 upstream Combine the various logic which goes through all those x86_cpu_id matching structures in one function. Suggested-by:
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Linus Torvalds authored
commit 1aa7a573 upstream The macro is not type safe and I did look for why that "g" constraint for the asm doesn't work: it's because the asm is more fundamentally wrong. It does movl %[val], %%eax but "val" isn't a 32-bit value, so then gcc will pass it in a register, and generate code like movl %rsi, %eax and gas will complain about a nonsensical 'mov' instruction (it's moving a 64-bit register to a 32-bit one). Passing it through memory will just hide the real bug - gcc still thinks the memory location is 64-bit, but the "movl" will only load the first 32 bits and it all happens to work because x86 is little-endian. Convert it to a type safe inline function with a little trick which hands the feature into the ALTERNATIVE macro. Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:
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David Woodhouse authored
commit def9331a upstream When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set on AMD cpus. This bug/feature bit is kind of special as it will be used very early when switching threads. Setting the bit and clearing it a little bit later leaves a critical window where things can go wrong. This time window has enlarged a little bit by using setup_clear_cpu_cap() instead of the hypervisor's set_cpu_features callback. It seems this larger window now makes it rather easy to hit the problem. The proper solution is to never set the bit in case of Xen. Signed-off-by:
Juergen Gross <jgross@suse.com> Reviewed-by:
Boris Ostrovsky <boris.ostrovsky@oracle.com> Acked-by:
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Juergen Gross authored
Upstream commit: 0808e80c ("xen: set cpu capabilities from xen_start_kernel()") There is no need to set the same capabilities for each cpu individually. This can easily be done for all cpus when starting the kernel. Signed-off-by:
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Mickaël Salaün authored
commit 505ce68c upstream Signed-off-by:
Mickaël Salaün <mic@digikod.net> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Kees Cook <keescook@chromium.org> Cc: Shuah Khan <shuahkh@osg.samsung.com> Cc: Will Drewry <wad@chromium.org> Acked-by:
Shuah Khan <shuahkh@osg.samsung.com> Signed-off-by:
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Mickaël Salaün authored
commit 6c045d07 upstream Rename SECCOMP_FLAG_FILTER_TSYNC to SECCOMP_FILTER_FLAG_TSYNC to match the UAPI. Signed-off-by:
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Alexander Sergeyev authored
commit e3b3121f upstream. In accordance with Intel's microcode revision guidance from March 6 MCU rev 0xc2 is cleared on both Skylake H/S and Skylake Xeon E3 processors that share CPUID 506E3. Signed-off-by:
Alexander Sergeyev <sergeev917@gmail.com> Signed-off-by:
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Ingo Molnar authored
commit d72f4e29 upstream. firmware_restrict_branch_speculation_*() recently started using preempt_enable()/disable(), but those are relatively high level primitives and cause build failures on some 32-bit builds. Since we want to keep <asm/nospec-branch.h> low level, convert them to macros to avoid header hell... Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: arjan.van.de.ven@intel.com Cc: bp@alien8.de Cc: dave.hansen@intel.com Cc: jmattson@google.com Cc: karahmed@amazon.de Cc: kvm@vger.kernel.org Cc: pbonzini@redhat.com Cc: rkrcmar@redhat.com Cc: linux-kernel@vger.kernel.org Signed-off-by:
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David Woodhouse authored
commit dd84441a upstream. Retpoline means the kernel is safe because it has no indirect branches. But firmware isn't, so use IBRS for firmware calls if it's available. Block preemption while IBRS is set, although in practice the call sites already had to be doing that. Ignore hpwdt.c for now. It's taking spinlocks and calling into firmware code, from an NMI handler. I don't want to touch that with a bargepole. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 36268223 upstream. As: 1) It's known that hypervisors lie about the environment anyhow (host mismatch) 2) Even if the hypervisor (Xen, KVM, VMWare, etc) provided a valid "correct" value, it all gets to be very murky when migration happens (do you provide the "new" microcode of the machine?). And in reality the cloud vendors are the ones that should make sure that the microcode that is running is correct and we should just sing lalalala and trust them. Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com> Cc: Wanpeng Li <kernellwp@gmail.com> Cc: kvm <kvm@vger.kernel.org> Cc: Krčmář <rkrcmar@redhat.com> Cc: Borislav Petkov <bp@alien8.de> CC: "H. Peter Anvin" <hpa@zytor.com> CC: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180226213019.GE9497@char.us.oracle.comSigned-off-by:
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Tim Chen authored
commit 18bf3c3e upstream. Flush indirect branches when switching into a process that marked itself non dumpable. This protects high value processes like gpg better, without having too high performance overhead. If done naïvely, we could switch to a kernel idle thread and then back to the original process, such as: process A -> idle -> process A In such scenario, we do not have to do IBPB here even though the process is non-dumpable, as we are switching back to the same process after a hiatus. To avoid the redundant IBPB, which is expensive, we track the last mm user context ID. The cost is to have an extra u64 mm context id to track the last mm we were using before switching to the init_mm used by idle. Avoiding the extra IBPB is probably worth the extra memory for this common scenario. For those cases where tlb_defer_switch_to_init_mm() returns true (non PCID), lazy tlb will defer switch to init_mm, so we will not be changing the mm for the process A -> idle -> process A switch. So IBPB will be skipped for this case. Thanks to the reviewers and Andy Lutomirski for the suggestion of using ctx_id which got rid of the problem of mm pointer recycling. Signed-off-by:
Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by:
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Andy Lutomirski authored
commit f39681ed upstream. This adds two new variables to mmu_context_t: ctx_id and tlb_gen. ctx_id uniquely identifies the mm_struct and will never be reused. For a given mm_struct (and hence ctx_id), tlb_gen is a monotonic count of the number of times that a TLB flush has been requested. The pair (ctx_id, tlb_gen) can be used as an identifier for TLB flush actions and will be used in subsequent patches to reliably determine whether all needed TLB flushes have occurred on a given CPU. This patch is split out for ease of review. By itself, it has no real effect other than creating and updating the new variables. Signed-off-by:
Andy Lutomirski <luto@kernel.org> Reviewed-by:
Nadav Amit <nadav.amit@gmail.com> Reviewed-by:
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Dave Hansen authored
commit 39a0526f upstream The arch-specific mm_context_t is a great place to put protection-key allocation state. But, we need to initialize the allocation state because pkey 0 is always "allocated". All of the runtime initialization of mm_context_t is done in *_ldt() manipulation functions. This renames the existing LDT functions like this: init_new_context() -> init_new_context_ldt() destroy_context() -> destroy_context_ldt() and makes init_new_context() and destroy_context() available for generic use. Signed-off-by:
Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by:
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Juergen Gross authored
commit 71c208dd upstream. Older Xen versions (4.5 and before) might have problems migrating pv guests with MSR_IA32_SPEC_CTRL having a non-zero value. So before suspending zero that MSR and restore it after being resumed. Signed-off-by:
Jan Beulich <jbeulich@suse.com> Cc: stable@vger.kernel.org Cc: xen-devel@lists.xenproject.org Cc: boris.ostrovsky@oracle.com Link: https://lkml.kernel.org/r/20180226140818.4849-1-jgross@suse.comSigned-off-by:
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Peter Zijlstra authored
commit ea00f301 upstream. Joe Konno reported a compile failure resulting from using an MSR without inclusion of <asm/msr-index.h>, and while the current code builds fine (by accident) this needs fixing for future patches. Reported-by:
Joe Konno <joe.konno@linux.intel.com> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: arjan@linux.intel.com Cc: bp@alien8.de Cc: dan.j.williams@intel.com Cc: dave.hansen@linux.intel.com Cc: dwmw2@infradead.org Cc: dwmw@amazon.co.uk Cc: gregkh@linuxfoundation.org Cc: hpa@zytor.com Cc: jpoimboe@redhat.com Cc: linux-tip-commits@vger.kernel.org Cc: luto@kernel.org Fixes: 20ffa1ca ("x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support") Link: http://lkml.kernel.org/r/20180213132819.GJ25201@hirez.programming.kicks-ass.netSigned-off-by:
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Dan Williams authored
commit be3233fb upstream. Allow the compiler to handle @size as an immediate value or memory directly rather than allocating a register. Reported-by:
Dan Williams <dan.j.williams@intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/151797010204.1289.1510000292250184993.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by:
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Ingo Molnar authored
commit 21e433bd upstream. Harmonize all the Spectre messages so that a: dmesg | grep -i spectre ... gives us most Spectre related kernel boot messages. Also fix a few other details: - clarify a comment about firmware speculation control - s/KPTI/PTI - remove various line-breaks that made the code uglier Acked-by:
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David Woodhouse authored
commit d37fc6d3 upstream. Arjan points out that the Intel document only clears the 0xc2 microcode on *some* parts with CPUID 506E3 (INTEL_FAM6_SKYLAKE_DESKTOP stepping 3). For the Skylake H/S platform it's OK but for Skylake E3 which has the same CPUID it isn't (yet) cleared. So removing it from the blacklist was premature. Put it back for now. Also, Arjan assures me that the 0x84 microcode for Kaby Lake which was featured in one of the early revisions of the Intel document was never released to the public, and won't be until/unless it is also validated as safe. So those can change to 0x80 which is what all *other* versions of the doc have identified. Once the retrospective testing of existing public microcodes is done, we should be back into a mode where new microcodes are only released in batches and we shouldn't even need to update the blacklist for those anyway, so this tweaking of the list isn't expected to be a thing which keeps happening. Requested-by:
Arjan van de Ven <arjan.van.de.ven@intel.com> Signed-off-by:
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David Woodhouse authored
commit 17513420 upstream. Intel have retroactively blessed the 0xc2 microcode on Skylake mobile and desktop parts, and the Gemini Lake 0x22 microcode is apparently fine too. We blacklisted the latter purely because it was present with all the other problematic ones in the 2018-01-08 release, but now it's explicitly listed as OK. We still list 0x84 for the various Kaby Lake / Coffee Lake parts, as that appeared in one version of the blacklist and then reverted to 0x80 again. We can change it if 0x84 is actually announced to be safe. Signed-off-by:
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Dan Williams authored
commit 6b8cf5cc upstream. At entry userspace may have populated registers with values that could otherwise be useful in a speculative execution attack. Clear them to minimize the kernel's attack surface. Originally-From: Andi Kleen <ak@linux.intel.com> Signed-off-by:
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Denys Vlasenko authored
commit 778843f9 upstream Use of a temporary R8 register here seems to be unnecessary. "push %r8" is a two-byte insn (it needs REX prefix to specify R8), "push $0" is two-byte too. It seems just using the latter would be no worse. Thus, code had an unnecessary "xorq %r8,%r8" insn. It probably costs nothing in execution time here since we are probably limited by store bandwidth at this point, but still. Run-tested under QEMU: 32-bit calls still work: / # ./test_syscall_vdso32 [RUN] Executing 6-argument 32-bit syscall via VDSO [OK] Arguments are preserved across syscall [NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn [OK] R8..R15 did not leak kernel data [RUN] Executing 6-argument 32-bit syscall via INT 80 [OK] Arguments are preserved across syscall [OK] R8..R15 did not leak kernel data [RUN] Running tests under ptrace [RUN] Executing 6-argument 32-bit syscall via VDSO [OK] Arguments are preserved across syscall [NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn [OK] R8..R15 did not leak kernel data [RUN] Executing 6-argument 32-bit syscall via INT 80 [OK] Arguments are preserved across syscall [OK] R8..R15 did not leak kernel data Signed-off-by:
Denys Vlasenko <dvlasenk@redhat.com> Acked-by:
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