Re: [PATCH 5.15 03/14] x86/speculation: Add a conditional CS prefix to CALL_NOSPEC

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 052040e34c08428a5a388b85787e8531970c0c67

Status in newer kernel trees:
6.14.y | Present (different SHA1: 9af9ad85ac44)
6.12.y | Present (different SHA1: 2d3bf48b14d4)
6.6.y | Present (different SHA1: 4dc248983ca5)
6.1.y | Present (different SHA1: fe6577881bf4)

Note: The patch differs from the upstream commit:
---
1:  052040e34c084 ! 1:  70b69b6a93bdd x86/speculation: Add a conditional CS prefix to CALL_NOSPEC
    @@ Metadata
      ## Commit message ##
         x86/speculation: Add a conditional CS prefix to CALL_NOSPEC
     
    +    commit 052040e34c08428a5a388b85787e8531970c0c67 upstream.
    +
         Retpoline mitigation for spectre-v2 uses thunks for indirect branches. To
         support this mitigation compilers add a CS prefix with
         -mindirect-branch-cs-prefix. For an indirect branch in asm, this needs to
    @@ arch/x86/include/asm/nospec-branch.h
       */
      .macro __CS_PREFIX reg:req
      	.irp rs,r8,r9,r10,r11,r12,r13,r14,r15
    -@@ arch/x86/include/asm/nospec-branch.h: static inline void call_depth_return_thunk(void) {}
    +@@ arch/x86/include/asm/nospec-branch.h: extern retpoline_thunk_t __x86_indirect_thunk_array[];
      
      #ifdef CONFIG_X86_64
      
    @@ arch/x86/include/asm/nospec-branch.h: static inline void call_depth_return_thunk
     +
      /*
       * Inline asm uses the %V modifier which is only in newer GCC
    -  * which is ensured when CONFIG_MITIGATION_RETPOLINE is defined.
    +  * which is ensured when CONFIG_RETPOLINE is defined.
       */
    - #ifdef CONFIG_MITIGATION_RETPOLINE
    + #ifdef CONFIG_RETPOLINE
     -#define CALL_NOSPEC	"call __x86_indirect_thunk_%V[thunk_target]\n"
     +#define CALL_NOSPEC	__CS_PREFIX("%V[thunk_target]")	\
     +			"call __x86_indirect_thunk_%V[thunk_target]\n"
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.1.y        |  Success    |  Success   |