Commit 010c4a46 authored by Pawan Gupta's avatar Pawan Gupta Committed by Ingo Molnar
Browse files

x86/speculation: Simplify and make CALL_NOSPEC consistent 



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: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarIngo 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
parent 7eb17214

arch/x86/include/asm/nospec-branch.h

+5 −10
Original line number Diff line number Diff line
@@ -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)