linux-kernel - [PATCH] x86/fpu: Delay instruction pointer fixup until after after warning

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Message-Id: <20250618193313.17F0EF2E@davehans-spike.ostc.intel.com>
Date: Wed, 18 Jun 2025 12:33:13 -0700
From: Dave Hansen <dave.hansen@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, tglx@...utronix.de, bp@...en8.de, mingo@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>, Chang S. Bae <chang.seok.bae@...el.com>, Eric Biggers <ebiggers@...gle.com>, Rik van Riel <riel@...hat.com>, stable@...r.kernel.org
Subject: [PATCH] x86/fpu: Delay instruction pointer fixup until after after warning

From: Dave Hansen <dave.hansen@...ux.intel.com>

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
e non-FPU-related instruction is #GP'ing.

Do not fix up RIP until after printing the warning.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Fixes: d5c8028b4788 ("x86/fpu: Reinitialize FPU registers if restoring FPU state fails")
Cc: stable@...r.kernel.org
Cc: Eric Biggers <ebiggers@...gle.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Chang S. Bae <chang.seok.bae@...el.com>
---

 b/arch/x86/mm/extable.c |    4 ++--
 1 file changed, 2 insertions(+), 2 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	2025-06-18 12:21:30.231719499 -0700
+++ b/arch/x86/mm/extable.c	2025-06-18 12:25:53.979954060 -0700
@@ -122,11 +122,11 @@ 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));

+	regs->ip = ex_fixup_addr(fixup);
+
 	fpu_reset_from_exception_fixup();
 	return true;
 }
_