* [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve
@ 2016-11-16 16:56 Yu-cheng Yu
2016-11-16 17:54 ` Borislav Petkov
2016-11-17 21:31 ` Dave Hansen
0 siblings, 2 replies; 5+ messages in thread
From: Yu-cheng Yu @ 2016-11-16 16:56 UTC (permalink / raw)
To: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner, Ingo Molnar
Cc: Yu-cheng Yu, Andy Lutomirski, Borislav Petkov, David Hansen,
Fenghua Yu, Ravi V. Shankar
Robert O'Callahan reported that after an execve PTRACE_GETREGSET
NT_X86_XSTATE continues to return the pre-exec register values
until the exec'ed task modifies FPU state. The test code is at
https://bugzilla.redhat.com/attachment.cgi?id=1164286.
What is happening is when eagerfpu is enabled, fpu__clear() did
not properly clear fpstate. Fix it by doing just that.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reported-by: Robert O'Callahan <robert@ocallahan.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
---
arch/x86/kernel/fpu/core.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4700401..4c203c4 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -521,14 +521,14 @@ void fpu__clear(struct fpu *fpu)
{
WARN_ON_FPU(fpu != ¤t->thread.fpu); /* Almost certainly an anomaly */
- if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
- /* FPU state will be reallocated lazily at the first use. */
- fpu__drop(fpu);
- } else {
- if (!fpu->fpstate_active) {
- fpu__activate_curr(fpu);
- user_fpu_begin();
- }
+ fpu__drop(fpu);
+
+ /*
+ * When eagerfpu is used, make sure fpstate is cleared and initialized.
+ */
+ if (use_eager_fpu()) {
+ fpu__activate_curr(fpu);
+ user_fpu_begin();
copy_init_fpstate_to_fpregs();
}
}
--
1.9.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve
2016-11-16 16:56 [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve Yu-cheng Yu
@ 2016-11-16 17:54 ` Borislav Petkov
2016-11-17 21:31 ` Dave Hansen
1 sibling, 0 replies; 5+ messages in thread
From: Borislav Petkov @ 2016-11-16 17:54 UTC (permalink / raw)
To: Yu-cheng Yu
Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner, Ingo Molnar,
Andy Lutomirski, David Hansen, Fenghua Yu, Ravi V. Shankar
On Wed, Nov 16, 2016 at 08:56:36AM -0800, Yu-cheng Yu wrote:
> Robert O'Callahan reported that after an execve PTRACE_GETREGSET
> NT_X86_XSTATE continues to return the pre-exec register values
> until the exec'ed task modifies FPU state. The test code is at
> https://bugzilla.redhat.com/attachment.cgi?id=1164286.
>
> What is happening is when eagerfpu is enabled, fpu__clear() did
> not properly clear fpstate. Fix it by doing just that.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reported-by: Robert O'Callahan <robert@ocallahan.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: David Hansen <dave.hansen@linux.intel.com>
> Cc: Fenghua Yu <fenghua.yu@intel.com>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
> ---
> arch/x86/kernel/fpu/core.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 4700401..4c203c4 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -521,14 +521,14 @@ void fpu__clear(struct fpu *fpu)
> {
> WARN_ON_FPU(fpu != ¤t->thread.fpu); /* Almost certainly an anomaly */
>
> - if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
> - /* FPU state will be reallocated lazily at the first use. */
> - fpu__drop(fpu);
> - } else {
> - if (!fpu->fpstate_active) {
> - fpu__activate_curr(fpu);
> - user_fpu_begin();
> - }
> + fpu__drop(fpu);
> +
> + /*
> + * When eagerfpu is used, make sure fpstate is cleared and initialized.
> + */
> + if (use_eager_fpu()) {
c592b5734706 ("x86/fpu: Remove use_eager_fpu()")
Please redo this patch against tip/master.
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve
2016-11-16 16:56 [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve Yu-cheng Yu
2016-11-16 17:54 ` Borislav Petkov
@ 2016-11-17 21:31 ` Dave Hansen
2016-11-17 22:18 ` Yu-cheng Yu
2016-11-21 9:40 ` Ingo Molnar
1 sibling, 2 replies; 5+ messages in thread
From: Dave Hansen @ 2016-11-17 21:31 UTC (permalink / raw)
To: Yu-cheng Yu, linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
Ingo Molnar
Cc: Andy Lutomirski, Borislav Petkov, Fenghua Yu, Ravi V. Shankar
On 11/16/2016 08:56 AM, Yu-cheng Yu wrote:
> Robert O'Callahan reported that after an execve PTRACE_GETREGSET
> NT_X86_XSTATE continues to return the pre-exec register values
> until the exec'ed task modifies FPU state. The test code is at
> https://bugzilla.redhat.com/attachment.cgi?id=1164286.
>
> What is happening is when eagerfpu is enabled, fpu__clear() did
> not properly clear fpstate. Fix it by doing just that.
Functionally, I think the patch is fine. just a few
comment/documentation nits.
I think fpu__clear()'s comments are a bit out of date. Could we make it
clear that it is invalidating both fpregs *and* fpstate?
I also think the
/* FPU state will be reallocated lazily at the first use. */"
comment was fairly valuable. Could we find some way to keep it?
The new comment:
> + /*
> + * When eagerfpu is used, make sure fpstate is cleared and initialized.
> + */
also kinda implies that the if() block is only messing with fpstate.
Could we make that more clear? Maybe by commenting the individual lines
inside the if():
> + if (use_eager_fpu()) {
> + fpu__activate_curr(fpu);
> + user_fpu_begin();
instead of having it above? Maybe something like:
if (use_eager_fpu()) {
/* activate and load init fpstate into 'fpu' */
fpu__activate_curr(fpu);
/* re-activate fpregs: */
user_fpu_begin();
/* take new init fpstate and place in fpregs: */
copy_init_fpstate_to_fpregs();
}
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve
2016-11-17 21:31 ` Dave Hansen
@ 2016-11-17 22:18 ` Yu-cheng Yu
2016-11-21 9:40 ` Ingo Molnar
1 sibling, 0 replies; 5+ messages in thread
From: Yu-cheng Yu @ 2016-11-17 22:18 UTC (permalink / raw)
To: Dave Hansen
Cc: linux-kernel, x86, H. Peter Anvin, Thomas Gleixner, Ingo Molnar,
Andy Lutomirski, Borislav Petkov, Fenghua Yu, Ravi V. Shankar
On Thu, Nov 17, 2016 at 01:31:57PM -0800, Dave Hansen wrote:
> Functionally, I think the patch is fine. just a few
> comment/documentation nits.
Thanks! I will wait for a few days for any comments that might come up
and fix all together.
Yu-cheng
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve
2016-11-17 21:31 ` Dave Hansen
2016-11-17 22:18 ` Yu-cheng Yu
@ 2016-11-21 9:40 ` Ingo Molnar
1 sibling, 0 replies; 5+ messages in thread
From: Ingo Molnar @ 2016-11-21 9:40 UTC (permalink / raw)
To: Dave Hansen
Cc: Yu-cheng Yu, linux-kernel, x86, H. Peter Anvin, Thomas Gleixner,
Ingo Molnar, Andy Lutomirski, Borislav Petkov, Fenghua Yu,
Ravi V. Shankar
* Dave Hansen <dave.hansen@linux.intel.com> wrote:
> On 11/16/2016 08:56 AM, Yu-cheng Yu wrote:
> > Robert O'Callahan reported that after an execve PTRACE_GETREGSET
> > NT_X86_XSTATE continues to return the pre-exec register values
> > until the exec'ed task modifies FPU state. The test code is at
> > https://bugzilla.redhat.com/attachment.cgi?id=1164286.
> >
> > What is happening is when eagerfpu is enabled, fpu__clear() did
> > not properly clear fpstate. Fix it by doing just that.
>
> Functionally, I think the patch is fine. just a few
> comment/documentation nits.
>
> I think fpu__clear()'s comments are a bit out of date. Could we make it
> clear that it is invalidating both fpregs *and* fpstate?
>
> I also think the
>
> /* FPU state will be reallocated lazily at the first use. */"
>
> comment was fairly valuable. Could we find some way to keep it?
>
> The new comment:
>
> > + /*
> > + * When eagerfpu is used, make sure fpstate is cleared and initialized.
> > + */
>
> also kinda implies that the if() block is only messing with fpstate.
> Could we make that more clear? Maybe by commenting the individual lines
> inside the if():
>
> > + if (use_eager_fpu()) {
> > + fpu__activate_curr(fpu);
> > + user_fpu_begin();
>
> instead of having it above? Maybe something like:
>
> if (use_eager_fpu()) {
> /* activate and load init fpstate into 'fpu' */
> fpu__activate_curr(fpu);
> /* re-activate fpregs: */
> user_fpu_begin();
> /* take new init fpstate and place in fpregs: */
> copy_init_fpstate_to_fpregs();
> }
I agree with these suggestions - but I'll apply the simple patch to x86/urgent -
which can then be backported as far as necessary, and then resolve the conflict
with the v4.10 tip:x86/fpu branch, and on top of that we can fix these details,
ok?
In particular I don't like it how non-obvious the semantics are from the function
names. I think we should try to improve the nomenclature instead of adding
comments to every line.
Thanks,
Ingo
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-11-16 16:56 [PATCH] x86/fpu: Fix invalid FPU ptrace state after execve Yu-cheng Yu
2016-11-16 17:54 ` Borislav Petkov
2016-11-17 21:31 ` Dave Hansen
2016-11-17 22:18 ` Yu-cheng Yu
2016-11-21 9:40 ` Ingo Molnar
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