• David Woodhouse's avatar
    x86/retpoline: Add initial retpoline support · 76b04384
    David Woodhouse authored
    Enable the use of -mindirect-branch=thunk-extern in newer GCC, and provide
    the corresponding thunks. Provide assembler macros for invoking the thunks
    in the same way that GCC does, from native and inline assembler.
    
    This adds X86_FEATURE_RETPOLINE and sets it by default on all CPUs. In
    some circumstances, IBRS microcode features may be used instead, and the
    retpoline can be disabled.
    
    On AMD CPUs if lfence is serialising, the retpoline can be dramatically
    simplified to a simple "lfence; jmp *\reg". A future patch, after it has
    been verified that lfence really is serialising in all circumstances, can
    enable this by setting the X86_FEATURE_RETPOLINE_AMD feature bit in addition
    to X86_FEATURE_RETPOLINE.
    
    Do not align the retpoline in the altinstr section, because there is no
    guarantee that it stays aligned when it's copied over the oldinstr during
    alternative patching.
    
    [ Andi Kleen: Rename the macros, add CONFIG_RETPOLINE option, export thunks]
    [ tglx: Put actual function CALL/JMP in front of the macros, convert to
      	symbolic labels ]
    [ dwmw2: Convert back to numeric labels, merge objtool fixes ]
    Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: default avatarArjan van de Ven <arjan@linux.intel.com>
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    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/1515707194-20531-4-git-send-email-dwmw@amazon.co.uk
    76b04384
cpufeatures.h 20.8 KB