[PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[He Zhe]

When 32-bit userspace application is running on 64-bit kernel, the 32-bit
syscall return code would be changed from u32 to u64 in regs_return_value
and then changed to s64. Hence the negative return code would be treated
as a positive number and results in a non-error in, for example, audit
like below.

type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
success=yes exit=4294967283

This patch forces the u32->s32->s64 for compat tasks.

Signed-off-by: He Zhe <zhe.he@windriver.com>
---
 include/linux/ptrace.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index b5ebf6c01292..bc3056fff8a6 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -260,7 +260,9 @@ static inline void ptrace_release_task(struct task_struct *task)
  * is an error value.  On some systems like ia64 and powerpc they have different
  * indicators of success/failure and must define their own.
  */
-#define is_syscall_success(regs) (!IS_ERR_VALUE((unsigned long)(regs_return_value(regs))))
+#define is_syscall_success(regs) (!IS_ERR_VALUE(is_compat_task() ? \
+	(unsigned long)(s64)(s32)(regs_return_value(regs)) : \
+	(unsigned long)(regs_return_value(regs))))
 #endif
 
 /*
-- 
2.17.1

Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[Oleg Nesterov]

Add audit maintainers...

On 04/14, He Zhe wrote:
>
> When 32-bit userspace application is running on 64-bit kernel, the 32-bit
> syscall return code would be changed from u32 to u64 in regs_return_value
> and then changed to s64. Hence the negative return code would be treated
> as a positive number and results in a non-error in, for example, audit
> like below.

Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
long, not u32.

Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
so this patch looks wrong anyway.

Oleg.

> type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
> success=yes exit=4294967283
> 
> This patch forces the u32->s32->s64 for compat tasks.
> 
> Signed-off-by: He Zhe <zhe.he@windriver.com>
> ---
>  include/linux/ptrace.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> index b5ebf6c01292..bc3056fff8a6 100644
> --- a/include/linux/ptrace.h
> +++ b/include/linux/ptrace.h
> @@ -260,7 +260,9 @@ static inline void ptrace_release_task(struct task_struct *task)
>   * is an error value.  On some systems like ia64 and powerpc they have different
>   * indicators of success/failure and must define their own.
>   */
> -#define is_syscall_success(regs) (!IS_ERR_VALUE((unsigned long)(regs_return_value(regs))))
> +#define is_syscall_success(regs) (!IS_ERR_VALUE(is_compat_task() ? \
> +	(unsigned long)(s64)(s32)(regs_return_value(regs)) : \
> +	(unsigned long)(regs_return_value(regs))))
>  #endif
>  
>  /*
> -- 
> 2.17.1
> 

RE: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[David Laight]

From: Oleg Nesterov
> Sent: 14 April 2021 16:08
> 
> Add audit maintainers...
> 
> On 04/14, He Zhe wrote:
> >
> > When 32-bit userspace application is running on 64-bit kernel, the 32-bit
> > syscall return code would be changed from u32 to u64 in regs_return_value
> > and then changed to s64. Hence the negative return code would be treated
> > as a positive number and results in a non-error in, for example, audit
> > like below.
> 
> Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
> long, not u32.
> 
> Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
> so this patch looks wrong anyway.

And, as with the other patch a x64_64 64bit process can make both types
of 32bit system call - so it needs to depend on the system call entry type
not any type of the task.

	David

> 
> Oleg.
> 
> > type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
> > success=yes exit=4294967283
> >
> > This patch forces the u32->s32->s64 for compat tasks.
> >
> > Signed-off-by: He Zhe <zhe.he@windriver.com>
> > ---
> >  include/linux/ptrace.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> > index b5ebf6c01292..bc3056fff8a6 100644
> > --- a/include/linux/ptrace.h
> > +++ b/include/linux/ptrace.h
> > @@ -260,7 +260,9 @@ static inline void ptrace_release_task(struct task_struct *task)
> >   * is an error value.  On some systems like ia64 and powerpc they have different
> >   * indicators of success/failure and must define their own.
> >   */
> > -#define is_syscall_success(regs) (!IS_ERR_VALUE((unsigned long)(regs_return_value(regs))))
> > +#define is_syscall_success(regs) (!IS_ERR_VALUE(is_compat_task() ? \
> > +	(unsigned long)(s64)(s32)(regs_return_value(regs)) : \
> > +	(unsigned long)(regs_return_value(regs))))
> >  #endif
> >
> >  /*
> > --
> > 2.17.1
> >

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[Oleg Nesterov]

On 04/14, David Laight wrote:
>
> From: Oleg Nesterov
> > Sent: 14 April 2021 16:08
> >
> > Add audit maintainers...
> >
> > On 04/14, He Zhe wrote:
> > >
> > > When 32-bit userspace application is running on 64-bit kernel, the 32-bit
> > > syscall return code would be changed from u32 to u64 in regs_return_value
> > > and then changed to s64. Hence the negative return code would be treated
> > > as a positive number and results in a non-error in, for example, audit
> > > like below.
> >
> > Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
> > long, not u32.
> >
> > Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
> > so this patch looks wrong anyway.
>
> And, as with the other patch a x64_64 64bit process can make both types
> of 32bit system call - so it needs to depend on the system call entry type
> not any type of the task.

I don't understand... but iirc is_compat_task() used to check TS_COMPAT and
this is what we need to detect the 32-bit syscall. But it looks deprecated,
I think in_compat_syscall() should be used instead.

But this doesn't matter, I still can't understand the problem.

Oleg.

RE: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[David Laight]

From: Oleg Nesterov
> Sent: 14 April 2021 17:56
> 
> On 04/14, David Laight wrote:
> >
> > From: Oleg Nesterov
> > > Sent: 14 April 2021 16:08
> > >
> > > Add audit maintainers...
> > >
> > > On 04/14, He Zhe wrote:
> > > >
> > > > When 32-bit userspace application is running on 64-bit kernel, the 32-bit
> > > > syscall return code would be changed from u32 to u64 in regs_return_value
> > > > and then changed to s64. Hence the negative return code would be treated
> > > > as a positive number and results in a non-error in, for example, audit
> > > > like below.
> > >
> > > Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
> > > long, not u32.
> > >
> > > Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
> > > so this patch looks wrong anyway.
> >
> > And, as with the other patch a x64_64 64bit process can make both types
> > of 32bit system call - so it needs to depend on the system call entry type
> > not any type of the task.
> 
> I don't understand... but iirc is_compat_task() used to check TS_COMPAT and
> this is what we need to detect the 32-bit syscall.

Not on X86_64.
The syscall entry code sets the type on the current system call entry.
So a process that is created as a 64bit process can make both i386
and x32 system calls as well as normal 64bit ones.

> But it looks deprecated,
> I think in_compat_syscall() should be used instead.

That does the right checks on x86.
Most code doesn't need to know about the subtle difference between
normal 32bit calls and x32 ones.

> But this doesn't matter, I still can't understand the problem.

Dunno, I only know the 'fix' is borked.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[He Zhe]

On 4/15/21 12:55 AM, Oleg Nesterov wrote:
> On 04/14, David Laight wrote:
>> From: Oleg Nesterov
>>> Sent: 14 April 2021 16:08
>>>
>>> Add audit maintainers...
>>>
>>> On 04/14, He Zhe wrote:
>>>> When 32-bit userspace application is running on 64-bit kernel, the 32-bit
>>>> syscall return code would be changed from u32 to u64 in regs_return_value
>>>> and then changed to s64. Hence the negative return code would be treated
>>>> as a positive number and results in a non-error in, for example, audit
>>>> like below.
>>> Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
>>> long, not u32.
>>>
>>> Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
>>> so this patch looks wrong anyway.
>> And, as with the other patch a x64_64 64bit process can make both types
>> of 32bit system call - so it needs to depend on the system call entry type
>> not any type of the task.
> I don't understand... but iirc is_compat_task() used to check TS_COMPAT and
> this is what we need to detect the 32-bit syscall. But it looks deprecated,
> I think in_compat_syscall() should be used instead.
>
> But this doesn't matter, I still can't understand the problem.

Sorry for not enough clarification.

This was found on an arm64 kernel running with 32-bit user-space application.
The arm64 version of regs_return_value returns unsigned long.

static inline unsigned long regs_return_value(struct pt_regs *regs)
{
        return regs->regs[0];
}

But when the syscall fails, with -13 in my case, the return code has been saved
as a 32 bit long negative number, 0x00000000FFFFFFF3, in regs[0] by the time
regs_return_value gets called in audit_syscall_exit.

Then in audit_syscall_exit, the return value of regs_return_value is changed to
a 64 bit signed long, from when on it is treated as a positive number.

Similarly in is_syscall_success, 0x00000000FFFFFFF3 would be out of error
number range, resulting in a "success".

These two patches are to do the sign extension.

David, thanks, is_compat_syscall should be the right one to use. I didn't notice
the difference between is_compat_syscall and is_compat_task and thought
is_compat_task would be harmless to other architectures.


Zhe

>
> Oleg.
>

Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

[Oleg Nesterov]

On 04/15, He Zhe wrote:
>
>
> On 4/15/21 12:55 AM, Oleg Nesterov wrote:
> > I think in_compat_syscall() should be used instead.
> >
> > But this doesn't matter, I still can't understand the problem.
>
> Sorry for not enough clarification.
>
> This was found on an arm64 kernel running with 32-bit user-space application.

OK, but then I think you should add the arm64 version of is_syscall_success()
into arch/arm4/include/asm/ptrace.h and do not touch the generic version ?

Something like arch/arm64/include/asm/syscall.h:syscall_get_error() which uses
is_compat_thread(). Perhaps you can even do

	#define is_syscall_success(regs)	\
		(syscall_get_error(current, regs) == 0)

Oleg.