6.12-stable review patch. If anyone has any objections, please let me know.
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From: Pawan Gupta pawan.kumar.gupta@linux.intel.com
commit cfceff8526a426948b53445c02bcb98453c7330d upstream.
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... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/nospec-branch.h | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -442,16 +442,11 @@ static inline void call_depth_return_thu * 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)