From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Kyle Huey <me@kylehuey.com>,
Robert O'Callahan <rocallahan@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>,
linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Mark Rutland <mark.rutland@arm.com>,
Keno Fischer <keno@juliacomputing.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm list <kvm@vger.kernel.org>,
Gabriel Krisman Bertazi <krisman@collabora.com>,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax
Date: Thu, 20 Aug 2020 14:09:15 -0700 [thread overview]
Message-ID: <202008201404.6A0D5736@keescook> (raw)
In-Reply-To: <87blj6ifo8.fsf@nanos.tec.linutronix.de>
On Wed, Aug 19, 2020 at 09:44:39PM +0200, Thomas Gleixner wrote:
> On Wed, Aug 19 2020 at 10:14, Kyle Huey wrote:
> > tl;dr: after 27d6b4d14f5c3ab21c4aef87dd04055a2d7adf14 ptracer
> > modifications to orig_ax in a syscall entry trace stop are not honored
> > and this breaks our code.
>
> My fault and I have no idead why none of the silly test cases
> noticed. Fix below.
Hmm, which were you trying? Looking just now, I see that the seccomp
selftests were failing for all their syscall-changing tests.
Regardless, I can confirm both the failure and the fix.
Reported-by: Kyle Huey <me@kylehuey.com>
Tested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
kernelci.org is *so* close to having the kernel selftests actually
running with their builds. :)
https://github.com/kernelci/kernelci-core/issues/331
-Kees
>
> Thanks,
>
> tglx
> ---
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 9852e0d62d95..fcae019158ca 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -65,7 +65,8 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
>
> syscall_enter_audit(regs, syscall);
>
> - return ret ? : syscall;
> + /* The above might have changed the syscall number */
> + return ret ? : syscall_get_nr(current, regs);
> }
>
> noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
--
Kees Cook
next prev parent reply other threads:[~2020-08-20 21:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-19 17:14 [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax Kyle Huey
2020-08-19 19:44 ` Thomas Gleixner
2020-08-20 17:26 ` Kyle Huey
2020-08-20 21:09 ` Kees Cook [this message]
2020-08-21 0:35 ` Thomas Gleixner
[not found] ` <87a6xzrr89.fsf@mpe.ellerman.id.au>
2020-09-11 18:58 ` Kees Cook
2020-09-12 0:10 ` Kees Cook
2020-09-13 7:44 ` Michael Ellerman
2020-09-13 18:27 ` Thomas Gleixner
2020-09-14 20:04 ` Kees Cook
2020-09-17 0:39 ` Michael Ellerman
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