x86/retpoline/entry: Convert entry assembler indirect jumps

CVE-2017-5715 (Spectre v2 retpoline)

commit 2641f08b upstream.

Convert indirect jumps in core 32/64bit entry assembler code to use
non-speculative sequences when CONFIG_RETPOLINE is enabled.

Don't use CALL_NOSPEC in entry_SYSCALL_64_fastpath because the return
address after the 'call' instruction must be *precisely* at the
.Lentry_SYSCALL_64_after_fastpath label for stub_ptregs_64 to work,
and the use of alternatives will mess that up unless we play horrid
games to prepend with NOPs and make the variants the same length. It's
not worth it; in the case where we ALTERNATIVE out the retpoline, the
first instruction at __x86.indirect_thunk.rax is going to be a bare
jmp *%rax anyway.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: Rik van Riel <riel@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: thomas.lendacky@amd.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Kees Cook <keescook@google.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: https://lkml.kernel.org/r/1515707194-20531-7-git-send-email-dwmw@amazon.co.ukSigned-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Razvan Ghitulete <rga@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 11ed3fa6214dc86c2e12331f0864260c76f01328)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/entry/entry_32.S

@@ -44,6 +44,7 @@
 #include <asm/alternative-asm.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/nospec-branch.h>
 
 	.section .entry.text, "ax"
 
@@ -226,7 +227,8 @@ ENTRY(ret_from_kernel_thread)
 	pushl	$0x0202				# Reset kernel eflags
 	popfl
 	movl	PT_EBP(%esp), %eax
-	call	*PT_EBX(%esp)
+	movl	PT_EBX(%esp), %edx
+	CALL_NOSPEC %edx
 	movl	$0, PT_EAX(%esp)
 
 	/*
@@ -938,7 +940,7 @@ error_code:
 	movl	%ecx, %es
 	TRACE_IRQS_OFF
 	movl	%esp, %eax			# pt_regs pointer
-	call	*%edi
+	CALL_NOSPEC %edi
 	jmp	ret_from_exception
 END(page_fault)
 

arch/x86/entry/entry_64.S

@@ -36,6 +36,7 @@
 #include <asm/smap.h>
 #include <asm/pgtable_types.h>
 #include <asm/kaiser.h>
+#include <asm/nospec-branch.h>
 #include <linux/err.h>
 
 /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
@@ -184,7 +185,13 @@ entry_SYSCALL_64_fastpath:
 #endif
 	ja	1f				/* return -ENOSYS (already in pt_regs->ax) */
 	movq	%r10, %rcx
+#ifdef CONFIG_RETPOLINE
+	movq	sys_call_table(, %rax, 8), %rax
+	call	__x86_indirect_thunk_rax
+#else
 	call	*sys_call_table(, %rax, 8)
+#endif
+
 	movq	%rax, RAX(%rsp)
 1:
 /*
@@ -276,7 +283,12 @@ tracesys_phase2:
 #endif
 	ja	1f				/* return -ENOSYS (already in pt_regs->ax) */
 	movq	%r10, %rcx			/* fixup for C */
+#ifdef CONFIG_RETPOLINE
+	movq	sys_call_table(, %rax, 8), %rax
+	call	__x86_indirect_thunk_rax
+#else
 	call	*sys_call_table(, %rax, 8)
+#endif
 	movq	%rax, RAX(%rsp)
 1:
 	/* Use IRET because user could have changed pt_regs->foo */
@@ -491,7 +503,7 @@ ENTRY(ret_from_fork)
 	 * nb: we depend on RESTORE_EXTRA_REGS above
 	 */
 	movq	%rbp, %rdi
-	call	*%rbx
+	CALL_NOSPEC %rbx
 	movl	$0, RAX(%rsp)
 	RESTORE_EXTRA_REGS
 	jmp	int_ret_from_sys_call