From: "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Borislav Petkov <bp@suse.de>, Rik van Riel <riel@surriel.com>,
Aubrey Li <aubrey.li@intel.com>,
Austin Clements <austin@google.com>,
Barret Rhoden <brho@google.com>,
Dave Hansen <dave.hansen@intel.com>,
David Chase <drchase@golang.org>,
"H. Peter Anvin" <hpa@zytor.com>,
ian@airs.com, Ingo Molnar <mingo@redhat.com>,
Josh Bleecher Snyder <josharian@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>, "x86-ml" <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/urgent] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx
Date: Thu, 28 Nov 2019 09:22:11 -0000 [thread overview]
Message-ID: <157493293150.21853.7731511969770345792.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20191128085306.hxfa2o3knqtu4wfn@linutronix.de>
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 59c4bd853abcea95eccc167a7d7fd5f1a5f47b98
Gitweb: https://git.kernel.org/tip/59c4bd853abcea95eccc167a7d7fd5f1a5f47b98
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Thu, 28 Nov 2019 09:53:06 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 28 Nov 2019 10:16:46 +01:00
x86/fpu: Don't cache access to fpu_fpregs_owner_ctx
The state/owner of the FPU is saved to fpu_fpregs_owner_ctx by pointing
to the context that is currently loaded. It never changed during the
lifetime of a task - it remained stable/constant.
After deferred FPU registers loading until return to userland was
implemented, the content of fpu_fpregs_owner_ctx may change during
preemption and must not be cached.
This went unnoticed for some time and was now noticed, in particular
since gcc 9 is caching that load in copy_fpstate_to_sigframe() and
reusing it in the retry loop:
copy_fpstate_to_sigframe()
load fpu_fpregs_owner_ctx and save on stack
fpregs_lock()
copy_fpregs_to_sigframe() /* failed */
fpregs_unlock()
*** PREEMPTION, another uses FPU, changes fpu_fpregs_owner_ctx ***
fault_in_pages_writeable() /* succeed, retry */
fpregs_lock()
__fpregs_load_activate()
fpregs_state_valid() /* uses fpu_fpregs_owner_ctx from stack */
copy_fpregs_to_sigframe() /* succeeds, random FPU content */
This is a comparison of the assembly produced by gcc 9, without vs with this
patch:
| # arch/x86/kernel/fpu/signal.c:173: if (!access_ok(buf, size))
| cmpq %rdx, %rax # tmp183, _4
| jb .L190 #,
|-# arch/x86/include/asm/fpu/internal.h:512: return fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
|-#APP
|-# 512 "arch/x86/include/asm/fpu/internal.h" 1
|- movq %gs:fpu_fpregs_owner_ctx,%rax #, pfo_ret__
|-# 0 "" 2
|-#NO_APP
|- movq %rax, -88(%rbp) # pfo_ret__, %sfp
…
|-# arch/x86/include/asm/fpu/internal.h:512: return fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
|- movq -88(%rbp), %rcx # %sfp, pfo_ret__
|- cmpq %rcx, -64(%rbp) # pfo_ret__, %sfp
|+# arch/x86/include/asm/fpu/internal.h:512: return fpu == this_cpu_read(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
|+#APP
|+# 512 "arch/x86/include/asm/fpu/internal.h" 1
|+ movq %gs:fpu_fpregs_owner_ctx(%rip),%rax # fpu_fpregs_owner_ctx, pfo_ret__
|+# 0 "" 2
|+# arch/x86/include/asm/fpu/internal.h:512: return fpu == this_cpu_read(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
|+#NO_APP
|+ cmpq %rax, -64(%rbp) # pfo_ret__, %sfp
Use this_cpu_read() instead this_cpu_read_stable() to avoid caching of
fpu_fpregs_owner_ctx during preemption points.
The Fixes: tag points to the commit where deferred FPU loading was
added. Since this commit, the compiler is no longer allowed to move the
load of fpu_fpregs_owner_ctx somewhere else / outside of the locked
section. A task preemption will change its value and stale content will
be observed.
[ bp: Massage. ]
Debugged-by: Austin Clements <austin@google.com>
Debugged-by: David Chase <drchase@golang.org>
Debugged-by: Ian Lance Taylor <ian@airs.com>
Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Rik van Riel <riel@surriel.com>
Tested-by: Borislav Petkov <bp@suse.de>
Cc: Aubrey Li <aubrey.li@intel.com>
Cc: Austin Clements <austin@google.com>
Cc: Barret Rhoden <brho@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Chase <drchase@golang.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: ian@airs.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Bleecher Snyder <josharian@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191128085306.hxfa2o3knqtu4wfn@linutronix.de
Link: https://bugzilla.kernel.org/show_bug.cgi?id=205663
---
arch/x86/include/asm/fpu/internal.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 4c95c36..44c48e3 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -509,7 +509,7 @@ static inline void __fpu_invalidate_fpregs_state(struct fpu *fpu)
static inline int fpregs_state_valid(struct fpu *fpu, unsigned int cpu)
{
- return fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
+ return fpu == this_cpu_read(fpu_fpregs_owner_ctx) && cpu == fpu->last_cpu;
}
/*
next prev parent reply other threads:[~2019-11-28 9:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-26 19:49 AVX register corruption from signal delivery Barret Rhoden
2019-11-26 20:20 ` Sebastian Andrzej Siewior
2019-11-26 21:23 ` Barret Rhoden
2019-11-26 22:13 ` Borislav Petkov
2019-11-26 22:30 ` Andy Lutomirski
2019-11-26 23:00 ` Borislav Petkov
2019-11-27 12:42 ` [PATCH] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx Sebastian Andrzej Siewior
2019-11-27 14:07 ` Borislav Petkov
2019-11-27 18:42 ` Barret Rhoden
2019-11-28 8:53 ` [PATCH v2] " Sebastian Andrzej Siewior
2019-11-28 9:22 ` tip-bot2 for Sebastian Andrzej Siewior [this message]
2019-11-29 16:57 ` David Laight
2019-11-29 17:08 ` 'Sebastian Andrzej Siewior'
2019-11-27 15:46 ` [PATCH] " Rik van Riel
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