x86/speculation: Simplify and make CALL_NOSPEC consistent

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_RETPOLINE is
enabled.

  [ pawan: s/CONFIG_MITIGATION_RETPOLINE/CONFIG_RETPOLINE/ ]

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index daf58a96e0a704b80751a24b7651e22fa4e41f28..7b5b93da50f59b48c6a0d257fd2db858d0bd8b2d 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -284,16 +284,11 @@ extern void (*x86_return_thunk)(void);
  * Inline asm uses the %V modifier which is only in newer GCC
  * which is ensured when CONFIG_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_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)