* [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
@ 2012-10-17 11:42 David Vrabel
2012-10-17 11:48 ` David Vrabel
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: David Vrabel @ 2012-10-17 11:42 UTC (permalink / raw)
To: xen-devel; +Cc: stable, Frediano Ziglio, David Vrabel, Konrad Rzeszutek Wilk
From: David Vrabel <david.vrabel@citrix.com>
In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
(-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
/and/ the process has a pending signal then %eip (and %eax) are
corrupted when returning to the main process after handling the
signal. The application may then crash with SIGSEGV or a SIGILL or it
may have subtly incorrect behaviour (depending on what instruction it
returned to).
The occurs because handle_signal() is incorrectly thinking that there
is a system call that needs to restarted so it adjusts %eip and %eax
to re-execute the system call instruction (even though user space had
not done a system call).
If %eax == -514 (-ERESTARTNOHAND (-514) or -ERESTART_RESTARTBLOCK
(-516) then handle_signal() only corrupted %eax (by setting it to
-EINTR). This may cause the application to crash or have incorrect
behaviour.
handle_signal() assumes that regs->orig_ax >= 0 means a system call so
any kernel entry point that is not for a system call must push a
negative value for orig_ax. For example, for physical interrupts on
bare metal the inverse of the vector is pushed and page_fault() sets
regs->orig_ax to -1, overwriting the hardware provided error code.
xen_hypervisor_callback() was incorrectly pushing 0 for orig_ax
instead of -1. For consistency, we also change
xen_failsafe_callback().
Classic Xen kernels pushed %eax which works as %eax cannot be both
non-negative and -RESTARTSYS (etc.), but using -1 avoids the
additional tests in handle_signal().
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: stable@kernel.org
---
arch/x86/kernel/entry_32.S | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2c63407..6a19e66 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1042,7 +1042,7 @@ ENTRY(xen_sysenter_target)
ENTRY(xen_hypervisor_callback)
CFI_STARTPROC
- pushl_cfi $0
+ pushl_cfi $-1 /* orig_ax = -1 => not a system call */
SAVE_ALL
TRACE_IRQS_OFF
@@ -1078,7 +1078,7 @@ ENDPROC(xen_hypervisor_callback)
# We distinguish between categories by maintaining a status value in EAX.
ENTRY(xen_failsafe_callback)
CFI_STARTPROC
- pushl_cfi %eax
+ pushl_cfi $-1 /* orig_ax = -1 => not a system call */
movl $1,%eax
1: mov 4(%esp),%ds
2: mov 8(%esp),%es
--
1.7.2.5
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
2012-10-17 11:42 [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler David Vrabel
@ 2012-10-17 11:48 ` David Vrabel
2012-10-17 11:52 ` Ian Campbell
2012-10-17 12:07 ` Jan Beulich
2 siblings, 0 replies; 6+ messages in thread
From: David Vrabel @ 2012-10-17 11:48 UTC (permalink / raw)
To: David Vrabel
Cc: Frediano Ziglio, Konrad Rzeszutek Wilk, stable@kernel.org,
xen-devel@lists.xen.org
On 17/10/12 12:42, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
>
> In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
> (-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
> /and/ the process has a pending signal then %eip (and %eax) are
> corrupted when returning to the main process after handling the
> signal. The application may then crash with SIGSEGV or a SIGILL or it
> may have subtly incorrect behaviour (depending on what instruction it
> returned to).
The following test program shows the bug. It will receive the signal
when in the infinite loop and return to the preceeding int 3 instruction.
Big thanks to Frediano for producing the test program and the majority
of the effort in tracking down this bug.
David
8<--------------------------
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <assert.h>
#include <sys/time.h>
static void handler(int sig)
{
static unsigned count = 0;
if (++count == 60 * 1000)
exit(0);
}
int main(void)
{
struct sigaction act;
// set signal
sigfillset(&act.sa_mask);
act.sa_flags = 0;
act.sa_handler = handler;
int err = sigaction(SIGALRM, &act, NULL);
assert(!err);
// set timer
struct itimerval ival = { { 0, 1000 }, { 0, 1000 } };
err = setitimer(ITIMER_REAL, &ival, NULL);
assert(!err);
#if !defined(__x86_64__) && !defined(__i386__)
# error This code work only on Intel architecture!
#endif
// wait for a core !!
asm(
#ifdef __x86_64__
" mov $-513, %rax\n"
#else
" mov $-513, %eax\n"
#endif
" jmp infinite\n"
" int $3\n"
" int $3\n"
" int $3\n"
" int $3\n"
"infinite:\n"
" jmp infinite\n"
);
return 0;
}
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
2012-10-17 11:42 [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler David Vrabel
2012-10-17 11:48 ` David Vrabel
@ 2012-10-17 11:52 ` Ian Campbell
2012-10-17 12:07 ` Jan Beulich
2 siblings, 0 replies; 6+ messages in thread
From: Ian Campbell @ 2012-10-17 11:52 UTC (permalink / raw)
To: David Vrabel
Cc: Frediano Ziglio, Konrad Rzeszutek Wilk, stable@kernel.org,
xen-devel@lists.xen.org
On Wed, 2012-10-17 at 12:42 +0100, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
>
> In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
> (-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
> /and/ the process has a pending signal then %eip (and %eax) are
> corrupted when returning to the main process after handling the
> signal. The application may then crash with SIGSEGV or a SIGILL or it
> may have subtly incorrect behaviour (depending on what instruction it
> returned to).
>
> The occurs because handle_signal() is incorrectly thinking that there
> is a system call that needs to restarted so it adjusts %eip and %eax
> to re-execute the system call instruction (even though user space had
> not done a system call).
>
> If %eax == -514 (-ERESTARTNOHAND (-514) or -ERESTART_RESTARTBLOCK
> (-516) then handle_signal() only corrupted %eax (by setting it to
> -EINTR). This may cause the application to crash or have incorrect
> behaviour.
>
> handle_signal() assumes that regs->orig_ax >= 0 means a system call so
> any kernel entry point that is not for a system call must push a
> negative value for orig_ax. For example, for physical interrupts on
> bare metal the inverse of the vector is pushed and page_fault() sets
> regs->orig_ax to -1, overwriting the hardware provided error code.
>
> xen_hypervisor_callback() was incorrectly pushing 0 for orig_ax
> instead of -1. For consistency, we also change
> xen_failsafe_callback().
>
> Classic Xen kernels pushed %eax which works as %eax cannot be both
> non-negative and -RESTARTSYS (etc.), but using -1 avoids the
> additional tests in handle_signal().
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: stable@kernel.org
> ---
> arch/x86/kernel/entry_32.S | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index 2c63407..6a19e66 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -1042,7 +1042,7 @@ ENTRY(xen_sysenter_target)
>
> ENTRY(xen_hypervisor_callback)
> CFI_STARTPROC
> - pushl_cfi $0
> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
> SAVE_ALL
> TRACE_IRQS_OFF
>
> @@ -1078,7 +1078,7 @@ ENDPROC(xen_hypervisor_callback)
> # We distinguish between categories by maintaining a status value in EAX.
> ENTRY(xen_failsafe_callback)
> CFI_STARTPROC
> - pushl_cfi %eax
> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
> movl $1,%eax
> 1: mov 4(%esp),%ds
> 2: mov 8(%esp),%es
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
2012-10-17 11:42 [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler David Vrabel
2012-10-17 11:48 ` David Vrabel
2012-10-17 11:52 ` Ian Campbell
@ 2012-10-17 12:07 ` Jan Beulich
2012-10-17 12:19 ` David Vrabel
2 siblings, 1 reply; 6+ messages in thread
From: Jan Beulich @ 2012-10-17 12:07 UTC (permalink / raw)
To: David Vrabel; +Cc: Frediano Ziglio, Konrad Rzeszutek Wilk, stable, xen-devel
>>> On 17.10.12 at 13:42, David Vrabel <david.vrabel@citrix.com> wrote:
> From: David Vrabel <david.vrabel@citrix.com>
>
> In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
> (-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
> /and/ the process has a pending signal then %eip (and %eax) are
> corrupted when returning to the main process after handling the
> signal. The application may then crash with SIGSEGV or a SIGILL or it
> may have subtly incorrect behaviour (depending on what instruction it
> returned to).
>
> The occurs because handle_signal() is incorrectly thinking that there
> is a system call that needs to restarted so it adjusts %eip and %eax
> to re-execute the system call instruction (even though user space had
> not done a system call).
>
> If %eax == -514 (-ERESTARTNOHAND (-514) or -ERESTART_RESTARTBLOCK
> (-516) then handle_signal() only corrupted %eax (by setting it to
> -EINTR). This may cause the application to crash or have incorrect
> behaviour.
>
> handle_signal() assumes that regs->orig_ax >= 0 means a system call so
> any kernel entry point that is not for a system call must push a
> negative value for orig_ax. For example, for physical interrupts on
> bare metal the inverse of the vector is pushed and page_fault() sets
> regs->orig_ax to -1, overwriting the hardware provided error code.
>
> xen_hypervisor_callback() was incorrectly pushing 0 for orig_ax
> instead of -1. For consistency, we also change
> xen_failsafe_callback().
Is this really just for consistency? There is a way for the failsafe
callback to continue to ret_from_exception, and I would think that
the same situation could arise there (and for the x86-64 case too).
Jan
> Classic Xen kernels pushed %eax which works as %eax cannot be both
> non-negative and -RESTARTSYS (etc.), but using -1 avoids the
> additional tests in handle_signal().
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> Cc: stable@kernel.org
> ---
> arch/x86/kernel/entry_32.S | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index 2c63407..6a19e66 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -1042,7 +1042,7 @@ ENTRY(xen_sysenter_target)
>
> ENTRY(xen_hypervisor_callback)
> CFI_STARTPROC
> - pushl_cfi $0
> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
> SAVE_ALL
> TRACE_IRQS_OFF
>
> @@ -1078,7 +1078,7 @@ ENDPROC(xen_hypervisor_callback)
> # We distinguish between categories by maintaining a status value in EAX.
> ENTRY(xen_failsafe_callback)
> CFI_STARTPROC
> - pushl_cfi %eax
> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
> movl $1,%eax
> 1: mov 4(%esp),%ds
> 2: mov 8(%esp),%es
> --
> 1.7.2.5
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
2012-10-17 12:07 ` Jan Beulich
@ 2012-10-17 12:19 ` David Vrabel
2012-10-17 12:28 ` Jan Beulich
0 siblings, 1 reply; 6+ messages in thread
From: David Vrabel @ 2012-10-17 12:19 UTC (permalink / raw)
To: Jan Beulich
Cc: Frediano Ziglio, Konrad Rzeszutek Wilk, xen-devel@lists.xen.org
On 17/10/12 13:07, Jan Beulich wrote:
>>>> On 17.10.12 at 13:42, David Vrabel <david.vrabel@citrix.com> wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
>> (-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
>> /and/ the process has a pending signal then %eip (and %eax) are
>> corrupted when returning to the main process after handling the
>> signal. The application may then crash with SIGSEGV or a SIGILL or it
>> may have subtly incorrect behaviour (depending on what instruction it
>> returned to).
>>
>> The occurs because handle_signal() is incorrectly thinking that there
>> is a system call that needs to restarted so it adjusts %eip and %eax
>> to re-execute the system call instruction (even though user space had
>> not done a system call).
>>
>> If %eax == -514 (-ERESTARTNOHAND (-514) or -ERESTART_RESTARTBLOCK
>> (-516) then handle_signal() only corrupted %eax (by setting it to
>> -EINTR). This may cause the application to crash or have incorrect
>> behaviour.
>>
>> handle_signal() assumes that regs->orig_ax >= 0 means a system call so
>> any kernel entry point that is not for a system call must push a
>> negative value for orig_ax. For example, for physical interrupts on
>> bare metal the inverse of the vector is pushed and page_fault() sets
>> regs->orig_ax to -1, overwriting the hardware provided error code.
>>
>> xen_hypervisor_callback() was incorrectly pushing 0 for orig_ax
>> instead of -1. For consistency, we also change
>> xen_failsafe_callback().
>
> Is this really just for consistency? There is a way for the failsafe
> callback to continue to ret_from_exception, and I would think that
> the same situation could arise there (and for the x86-64 case too).
The 32-bit xen_failsafe_callback was using %eax for orig_ax which is
safe (see comment on classic kernel behaviour below).
We couldn't repro the issue in 64-bit guests and looking at entry_64.S
xen_hypervisor_callback is correct (see the zeroentry macro).
I must admit to not really being able to follow what
xen_failsafe_callback is doing, but it does look like that last pushq
before the SAVE_ALL should be pushq_cfi $-1 as well. Do you agree?
David
>> Classic Xen kernels pushed %eax which works as %eax cannot be both
>> non-negative and -RESTARTSYS (etc.), but using -1 avoids the
>> additional tests in handle_signal().
>>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>> Cc: stable@kernel.org
>> ---
>> arch/x86/kernel/entry_32.S | 4 ++--
>> 1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
>> index 2c63407..6a19e66 100644
>> --- a/arch/x86/kernel/entry_32.S
>> +++ b/arch/x86/kernel/entry_32.S
>> @@ -1042,7 +1042,7 @@ ENTRY(xen_sysenter_target)
>>
>> ENTRY(xen_hypervisor_callback)
>> CFI_STARTPROC
>> - pushl_cfi $0
>> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
>> SAVE_ALL
>> TRACE_IRQS_OFF
>>
>> @@ -1078,7 +1078,7 @@ ENDPROC(xen_hypervisor_callback)
>> # We distinguish between categories by maintaining a status value in EAX.
>> ENTRY(xen_failsafe_callback)
>> CFI_STARTPROC
>> - pushl_cfi %eax
>> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
>> movl $1,%eax
>> 1: mov 4(%esp),%ds
>> 2: mov 8(%esp),%es
>> --
>> 1.7.2.5
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
>
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler
2012-10-17 12:19 ` David Vrabel
@ 2012-10-17 12:28 ` Jan Beulich
0 siblings, 0 replies; 6+ messages in thread
From: Jan Beulich @ 2012-10-17 12:28 UTC (permalink / raw)
To: David Vrabel
Cc: Frediano Ziglio, Konrad Rzeszutek Wilk, xen-devel@lists.xen.org
>>> On 17.10.12 at 14:19, David Vrabel <david.vrabel@citrix.com> wrote:
> On 17/10/12 13:07, Jan Beulich wrote:
>>>>> On 17.10.12 at 13:42, David Vrabel <david.vrabel@citrix.com> wrote:
>>> From: David Vrabel <david.vrabel@citrix.com>
>>>
>>> In 32 bit guests, if a userspace process has %eax == -ERESTARTSYS
>>> (-512) or -ERESTARTNOINTR (-513) when it is interrupted by an event
>>> /and/ the process has a pending signal then %eip (and %eax) are
>>> corrupted when returning to the main process after handling the
>>> signal. The application may then crash with SIGSEGV or a SIGILL or it
>>> may have subtly incorrect behaviour (depending on what instruction it
>>> returned to).
>>>
>>> The occurs because handle_signal() is incorrectly thinking that there
>>> is a system call that needs to restarted so it adjusts %eip and %eax
>>> to re-execute the system call instruction (even though user space had
>>> not done a system call).
>>>
>>> If %eax == -514 (-ERESTARTNOHAND (-514) or -ERESTART_RESTARTBLOCK
>>> (-516) then handle_signal() only corrupted %eax (by setting it to
>>> -EINTR). This may cause the application to crash or have incorrect
>>> behaviour.
>>>
>>> handle_signal() assumes that regs->orig_ax >= 0 means a system call so
>>> any kernel entry point that is not for a system call must push a
>>> negative value for orig_ax. For example, for physical interrupts on
>>> bare metal the inverse of the vector is pushed and page_fault() sets
>>> regs->orig_ax to -1, overwriting the hardware provided error code.
>>>
>>> xen_hypervisor_callback() was incorrectly pushing 0 for orig_ax
>>> instead of -1. For consistency, we also change
>>> xen_failsafe_callback().
>>
>> Is this really just for consistency? There is a way for the failsafe
>> callback to continue to ret_from_exception, and I would think that
>> the same situation could arise there (and for the x86-64 case too).
>
> The 32-bit xen_failsafe_callback was using %eax for orig_ax which is
> safe (see comment on classic kernel behaviour below).
Ah, yes, I didn't spot that %eax was used there instead of 0
(and other than inn the classic Xen kernel, which I will want to
fix too).
> We couldn't repro the issue in 64-bit guests and looking at entry_64.S
> xen_hypervisor_callback is correct (see the zeroentry macro).
Yes, the normal callback path isn't affected there.
> I must admit to not really being able to follow what
> xen_failsafe_callback is doing, but it does look like that last pushq
> before the SAVE_ALL should be pushq_cfi $-1 as well. Do you agree?
That's what I was trying to hint at. Feel free to put my ack on
the patch if you re-submit with that adjustment (and ideally the
commit message adjusted too).
Jan
>>> Classic Xen kernels pushed %eax which works as %eax cannot be both
>>> non-negative and -RESTARTSYS (etc.), but using -1 avoids the
>>> additional tests in handle_signal().
>>>
>>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>>> Cc: stable@kernel.org
>>> ---
>>> arch/x86/kernel/entry_32.S | 4 ++--
>>> 1 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
>>> index 2c63407..6a19e66 100644
>>> --- a/arch/x86/kernel/entry_32.S
>>> +++ b/arch/x86/kernel/entry_32.S
>>> @@ -1042,7 +1042,7 @@ ENTRY(xen_sysenter_target)
>>>
>>> ENTRY(xen_hypervisor_callback)
>>> CFI_STARTPROC
>>> - pushl_cfi $0
>>> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
>>> SAVE_ALL
>>> TRACE_IRQS_OFF
>>>
>>> @@ -1078,7 +1078,7 @@ ENDPROC(xen_hypervisor_callback)
>>> # We distinguish between categories by maintaining a status value in EAX.
>>> ENTRY(xen_failsafe_callback)
>>> CFI_STARTPROC
>>> - pushl_cfi %eax
>>> + pushl_cfi $-1 /* orig_ax = -1 => not a system call */
>>> movl $1,%eax
>>> 1: mov 4(%esp),%ds
>>> 2: mov 8(%esp),%es
>>> --
>>> 1.7.2.5
>>>
>>>
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@lists.xen.org
>>> http://lists.xen.org/xen-devel
>>
>>
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-10-17 12:28 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2012-10-17 11:42 [PATCH] xen/x86: don't corrupt %eip when returning from a signal handler David Vrabel
2012-10-17 11:48 ` David Vrabel
2012-10-17 11:52 ` Ian Campbell
2012-10-17 12:07 ` Jan Beulich
2012-10-17 12:19 ` David Vrabel
2012-10-17 12:28 ` Jan Beulich
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