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

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Message-ID: <20210414165547.GA22294@redhat.com>
Date:   Wed, 14 Apr 2021 18:55:47 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     He Zhe <zhe.he@...driver.com>, Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code
 handling for compat task

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.