iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/retpoline: Do the necessary fixup to the Zen3/4 srso return thunk for !SRSO

Browse Source 
commit 0e110732473e14d6520e49d75d2c88ef7d46fe67 upstream.

The srso_alias_untrain_ret() dummy thunk in the !CONFIG_MITIGATION_SRSO
case is there only for the altenative in CALL_UNTRAIN_RET to have
a symbol to resolve.

However, testing with kernels which don't have CONFIG_MITIGATION_SRSO
enabled, leads to the warning in patch_return() to fire:

  missing return thunk: srso_alias_untrain_ret+0x0/0x10-0x0: eb 0e 66 66 2e
  WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:826 apply_returns (arch/x86/kernel/alternative.c:826

Put in a plain "ret" there so that gcc doesn't put a return thunk in
in its place which special and gets checked.

In addition:

  ERROR: modpost: "srso_alias_untrain_ret" [arch/x86/kvm/kvm-amd.ko] undefined!
  make[2]: *** [scripts/Makefile.modpost:145: Module.symvers] Chyba 1
  make[1]: *** [/usr/src/linux-6.8.3/Makefile:1873: modpost] Chyba 2
  make: *** [Makefile:240: __sub-make] Chyba 2

since !SRSO builds would use the dummy return thunk as reported by
petr.pisar@atlas.cz, https://bugzilla.kernel.org/show_bug.cgi?id=218679.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202404020901.da75a60f-oliver.sang@intel.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/all/202404020901.da75a60f-oliver.sang@intel.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Borislav Petkov (AMD) 2024-04-02 16:05:49 +02:00 committed by Greg Kroah-Hartman
parent 668b3074aa
commit 3ec21104c8
1 changed files with 4 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/lib/retpoline.S
View File

@ -222,8 +222,11 @@ SYM_CODE_END(srso_return_thunk)
#define JMP_SRSO_UNTRAIN_RET "ud2"
/* Dummy for the alternative in CALL_UNTRAIN_RET. */
SYM_CODE_START(srso_alias_untrain_ret)
RET
ANNOTATE_UNRET_SAFE
ret
int3
SYM_FUNC_END(srso_alias_untrain_ret)
__EXPORT_THUNK(srso_alias_untrain_ret)
#endif /* CONFIG_CPU_SRSO */
#ifdef CONFIG_CPU_UNRET_ENTRY