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From: Andy Lutomirski <luto@kernel.org>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
	Oleg Nesterov <oleg@redhat.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Brian Gerst <brgerst@gmail.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v2 04/12] x86/entry/32: Restore FLAGS on SYSEXIT
Date: Wed,  9 Mar 2016 19:00:27 -0800	[thread overview]
Message-ID: <3f98b207472dc9784838eb5ca2b89dcc845ce269.1457578375.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1457578375.git.luto@kernel.org>
In-Reply-To: <cover.1457578375.git.luto@kernel.org>

We weren't restoring FLAGS at all on SYSEXIT.  Apparently no one cared.

With this patch applied, native kernels should always honor
task_pt_regs()->flags, which opens the door for some sys_iopl
cleanups.  I'll do those as a separate series, though, since getting
it right will involve tweaking some paravirt ops.

(The short version is that, before this patch, sys_iopl, invoked via
 SYSENTER, wasn't guaranteed to ever transfer the updated
 regs->flags, so sys_iopl had to change the hardware flags register
 as well.)

Reported-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/entry/entry_32.S | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 86665f93ff5d..d1437fdbf597 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -343,6 +343,15 @@ sysenter_past_esp:
 	popl	%eax			/* pt_regs->ax */
 
 	/*
+	 * Restore all flags except IF (we restore IF separately because
+	 * STI gives a one-instruction window in which we won't be interrupted,
+	 * whereas POPF does not.
+	 */
+	addl	$PT_EFLAGS-PT_DS, %esp	/* point esp at pt_regs->flags */
+	btr	$X86_EFLAGS_IF_BIT, (%esp)
+	popfl
+
+	/*
 	 * Return back to the vDSO, which will pop ecx and edx.
 	 * Don't bother with DS and ES (they already contain __USER_DS).
 	 */
-- 
2.5.0

  parent reply	other threads:[~2016-03-10  3:01 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-10  3:00 [PATCH v2 00/12] x86: Various SYSENTER/SYSEXIT/#DB fixes and cleanups Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 01/12] selftests/x86: In syscall_nt, test NT|TF as well Andy Lutomirski
2016-03-10 11:00   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 02/12] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test Andy Lutomirski
2016-03-10 11:01   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 03/12] x86/entry/32: Filter NT and speed up AC filtering in SYSENTER Andy Lutomirski
2016-03-10 11:01   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` Andy Lutomirski [this message]
2016-03-10 11:01   ` [tip:x86/asm] x86/entry/32: Restore FLAGS on SYSEXIT tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 05/12] x86/traps: Clear TIF_BLOCKSTEP on all debug exceptions Andy Lutomirski
2016-03-10 11:02   ` [tip:x86/asm] x86/entry/traps: " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 06/12] x86/traps: Clear DR6 early in do_debug and improve the comment Andy Lutomirski
2016-03-10 11:02   ` [tip:x86/asm] x86/entry/traps: Clear DR6 early in do_debug() " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 07/12] x86/entry: Vastly simplify SYSENTER TF handling Andy Lutomirski
2016-03-10 11:03   ` [tip:x86/asm] x86/entry: Vastly simplify SYSENTER TF (single-step) handling tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 08/12] x86/entry: Only allocate space for SYSENTER_stack if needed Andy Lutomirski
2016-03-10 11:03   ` [tip:x86/asm] x86/entry: Only allocate space for tss_struct::SYSENTER_stack " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 09/12] x86/entry/32: Simplify and fix up the SYSENTER stack #DB/NMI fixup Andy Lutomirski
2016-03-10 11:03   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 10/12] x86/entry/32: Add and check a stack canary for the SYSENTER stack Andy Lutomirski
2016-03-10 11:04   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 11/12] x86/entry: Remove TIF_SINGLESTEP entry work Andy Lutomirski
2016-03-10 11:04   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-03-10  3:00 ` [PATCH v2 12/12] x86/entry: Improve system call entry comments Andy Lutomirski
2016-03-10 11:05   ` [tip:x86/asm] " tip-bot for Andy Lutomirski

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