linux-kernel - Re: [PATCH] x86: General protection fault after STR (32 bit systems only)

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Message-ID: <20150612083625.GA22760@gmail.com>
Date:	Fri, 12 Jun 2015 10:36:25 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, X86 ML <x86@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: General protection fault after STR (32 bit systems
 only)


* H. Peter Anvin <hpa@...or.com> wrote:

> %es is used implicitly by string instructions.

Ok, so we are probably better off reloading ES as well early, right
when we return from the firmware, just in case something does
a copy before we hit the ES restore in restore_processor_state(),
which is a generic C function?

Something like the patch below?

I also added FS/GS/SS reloading to make it complete. If this (or a variant 
thereof, it's still totally untested) works then we can remove the segment 
save/restore layer in __save/restore_processor_state().

Thanks,

	Ingo

===========>
 arch/x86/kernel/acpi/wakeup_32.S | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
index 665c6b7d2ea9..1376a7fc21b7 100644
--- a/arch/x86/kernel/acpi/wakeup_32.S
+++ b/arch/x86/kernel/acpi/wakeup_32.S
@@ -61,6 +61,19 @@ ENTRY(wakeup_pmode_return)
 
 
 restore_registers:
+	/*
+	 * In case the BIOS corrupted our segment descriptors,
+	 * reload them to clear out any shadow descriptor
+	 * state:
+	 */
+	movl	$__USER_DS, %eax
+	movl	%eax, %ds
+	movl	%eax, %es
+	movl	%eax, %fs
+	movl	%eax, %gs
+	movl	$__KERNEL_DS, %eax
+	movl	%eax, %ss
+
 	movl	saved_context_ebp, %ebp
 	movl	saved_context_ebx, %ebx
 	movl	saved_context_esi, %esi
--
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