From 5d31174f3c8c465d9dbe88f6b9d1fe5716f44981 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Fri, 15 Mar 2024 09:18:23 +0100 Subject: [PATCH] x86/fpu: Fix AMD X86_BUG_FXSAVE_LEAK fixup The assembly snippet in restore_fpregs_from_fpstate() that implements X86_BUG_FXSAVE_LEAK fixup loads the value from a random variable, preferably the one that is already in the L1 cache. However, the access to fpinit_state via *fpstate pointer is not implemented correctly. The "m" asm constraint requires dereferenced pointer variable, otherwise the compiler just reloads the value via temporary stack slot. The current asm code reflects this: mov %rdi,(%rsp) ... fildl (%rsp) With dereferenced pointer variable, the code does what the comment above the asm snippet says: fildl (%rdi) Also, remove the pointless %P operand modifier. The modifier is ineffective on non-symbolic references - it was used to prevent %rip-relative addresses in .altinstr sections, but FILDL in the .text section can use %rip-relative addresses without problems. Signed-off-by: Uros Bizjak Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Linus Torvalds Link: https://lore.kernel.org/r/20240315081849.5187-1-ubizjak@gmail.com --- arch/x86/kernel/fpu/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 520deb411a70..1209c7aebb21 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -145,8 +145,8 @@ void restore_fpregs_from_fpstate(struct fpstate *fpstate, u64 mask) asm volatile( "fnclex\n\t" "emms\n\t" - "fildl %P[addr]" /* set F?P to defined value */ - : : [addr] "m" (fpstate)); + "fildl %[addr]" /* set F?P to defined value */ + : : [addr] "m" (*fpstate)); } if (use_xsave()) {