[PATCH] [v2] x86/fpu: Delay instruction pointer fixup until after warning

[Dave Hansen]

Changes from v1:
 * Fix minor typos
 * Use the more generic and standard ex_handler_default(). Had the
   original code used this helper, the bug would not have been there
   in the first place.

--

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Right now, if XRSTOR fails a console message like this is be printed:

	Bad FPU state detected at restore_fpregs_from_fpstate+0x9a/0x170, reinitializing FPU registers.

However, the text location (...+0x9a in this case) is the instruction
*AFTER* the XRSTOR. The highlighted instruction in the "Code:" dump
also points one instruction late.

The reason is that the "fixup" moves RIP up to pass the bad XRSTOR and
keep on running after returning from the #GP handler. But it does this
fixup before warning.

The resulting warning output is nonsensical because it looks like the
non-FPU-related instruction is #GP'ing.

Do not fix up RIP until after printing the warning. Do this by using
the more generic and standard ex_handler_default().

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Fixes: d5c8028b4788 ("x86/fpu: Reinitialize FPU registers if restoring FPU state fails")
Acked-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
---

 b/arch/x86/mm/extable.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff -puN arch/x86/mm/extable.c~fixup-fpu-gp-ip-later arch/x86/mm/extable.c
--- a/arch/x86/mm/extable.c~fixup-fpu-gp-ip-later	2025-06-24 13:58:09.722855233 -0700
+++ b/arch/x86/mm/extable.c	2025-06-24 13:58:09.736856435 -0700
@@ -122,13 +122,12 @@ static bool ex_handler_sgx(const struct
 static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 				 struct pt_regs *regs)
 {
-	regs->ip = ex_fixup_addr(fixup);
-
 	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
 		  (void *)instruction_pointer(regs));
 
 	fpu_reset_from_exception_fixup();
-	return true;
+
+	return ex_handler_default(fixup, regs);
 }
 
 /*
_