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x86/speculation: Simplify and make CALL_NOSPEC consistent

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CALL_NOSPEC macro is used to generate Spectre-v2 mitigation friendly
indirect branches. At compile time the macro defaults to indirect branch,
and at runtime those can be patched to thunk based mitigations.

This approach is opposite of what is done for the rest of the kernel, where
the compile time default is to replace indirect calls with retpoline thunk
calls.

Make CALL_NOSPEC consistent with the rest of the kernel, default to
retpoline thunk at compile time when CONFIG_MITIGATION_RETPOLINE is
enabled.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250228-call-nospec-v3-1-96599fed0f33@linux.intel.com
This commit is contained in:
Pawan Gupta 2025-02-28 18:35:43 -08:00 • committed by Ingo Molnar
parent 7eb172143d
commit 010c4a461c
1 changed files with 5 additions and 10 deletions
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15
arch/x86/include/asm/nospec-branch.h
View file

@ -424,16 +424,11 @@ static inline void call_depth_return_thunk(void) {}
* Inline asm uses the %V modifier which is only in newer GCC
* which is ensured when CONFIG_MITIGATION_RETPOLINE is defined.
*/
# define CALL_NOSPEC \
ALTERNATIVE_2( \
ANNOTATE_RETPOLINE_SAFE \
"call *%[thunk_target]\n", \
"call __x86_indirect_thunk_%V[thunk_target]\n", \
X86_FEATURE_RETPOLINE, \
"lfence;\n" \
ANNOTATE_RETPOLINE_SAFE \
"call *%[thunk_target]\n", \
X86_FEATURE_RETPOLINE_LFENCE)
#ifdef CONFIG_MITIGATION_RETPOLINE
#define CALL_NOSPEC "call __x86_indirect_thunk_%V[thunk_target]\n"
#else
#define CALL_NOSPEC "call *%[thunk_target]\n"
#endif
# define THUNK_TARGET(addr) [thunk_target] "r" (addr)