This is a note to let you know that I've just added the patch titled
x86/fsgsbase/64: Fully initialize FS and GS state in start_thread_common
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-fsgsbase-64-fully-initialize-fs-and-gs-state-in-start_thread_common.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 767d035d838f4fd6b5a5bbd7a3f6d293b7f65a49 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Tue, 1 Aug 2017 07:11:34 -0700
Subject: x86/fsgsbase/64: Fully initialize FS and GS state in start_thread_common
From: Andy Lutomirski <luto@xxxxxxxxxx>
commit 767d035d838f4fd6b5a5bbd7a3f6d293b7f65a49 upstream.
execve used to leak FSBASE and GSBASE on AMD CPUs. Fix it.
The security impact of this bug is small but not quite zero -- it
could weaken ASLR when a privileged task execs a less privileged
program, but only if program changed bitness across the exec, or the
child binary was highly unusual or actively malicious. A child
program that was compromised after the exec would not have access to
the leaked base.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bpetkov@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Chang Seok <chang.seok.bae@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/process_64.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -216,10 +216,19 @@ start_thread_common(struct pt_regs *regs
unsigned long new_sp,
unsigned int _cs, unsigned int _ss, unsigned int _ds)
{
+ WARN_ON_ONCE(regs != current_pt_regs());
+
+ if (static_cpu_has(X86_BUG_NULL_SEG)) {
+ /* Loading zero below won't clear the base. */
+ loadsegment(fs, __USER_DS);
+ load_gs_index(__USER_DS);
+ }
+
loadsegment(fs, 0);
loadsegment(es, _ds);
loadsegment(ds, _ds);
load_gs_index(0);
+
regs->ip = new_ip;
regs->sp = new_sp;
regs->cs = _cs;
Patches currently in stable-queue which might be from luto@xxxxxxxxxx are
queue-4.9/x86-switch_to-64-rewrite-fs-gs-switching-yet-again-to-fix-amd-cpus.patch
queue-4.9/x86-fsgsbase-64-fully-initialize-fs-and-gs-state-in-start_thread_common.patch
queue-4.9/x86-fsgsbase-64-report-fsbase-and-gsbase-correctly-in-core-dumps.patch