Messages in this thread | | | Date | Tue, 27 Feb 2024 10:47:57 +0200 | Subject | Re: [PATCH] x86/bugs: Use fixed addressing for VERW operand | From | Nikolay Borisov <> |
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On 27.02.24 г. 1:52 ч., Pawan Gupta wrote: > Macro used for MDS mitigation executes VERW with relative addressing for > the operand. This is unnecessary and creates a problem for backports on > older kernels that don't support relocations in alternatives. Relocation > support was added by commit 270a69c4485d ("x86/alternative: Support > relocations in alternatives"). Also asm for fixed addressing is much > more cleaner than relative RIP addressing. > > Simplify the asm by using fixed addressing for VERW operand. > > Fixes: baf8361e5455 ("x86/bugs: Add asm helpers for executing VERW") > Reported-by: Nikolay Borisov <nik.borisov@suse.com> > Closes: https://lore.kernel.org/lkml/20558f89-299b-472e-9a96-171403a83bd6@suse.com/ > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> > --- > arch/x86/include/asm/nospec-branch.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > index 2aa52cab1e46..ab19c7f1167b 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -323,7 +323,7 @@ > * Note: Only the memory operand variant of VERW clears the CPU buffers. > */ > .macro CLEAR_CPU_BUFFERS > - ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF > + ALTERNATIVE "", __stringify(verw mds_verw_sel), X86_FEATURE_CLEAR_CPU_BUF
Actually thinking about it more and discussing with Jiri (cc'ed), will this work with KASLR enabled?
> .endm > > #else /* __ASSEMBLY__ */ > > --- > base-commit: d206a76d7d2726f3b096037f2079ce0bd3ba329b > change-id: 20240226-verw-arg-fix-796a63088c4d >
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