From: Michael Ellerman <mpe@ellerman.id.au>
To: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
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>,
Kyle Huey <me@kylehuey.com>
Subject: Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax
Date: Sun, 13 Sep 2020 17:44:09 +1000 [thread overview]
Message-ID: <87d02qqfxy.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <202009111609.61E7875B3@keescook>
Kees Cook <keescook@chromium.org> writes:
> On Wed, Sep 09, 2020 at 11:53:42PM +1000, Michael Ellerman wrote:
>> I can observe the difference between v5.8 and mainline, using the
>> raw_syscall trace event and running the seccomp_bpf selftest which turns
>> a getpid (39) into a getppid (110).
>>
>> With v5.8 we see getppid on entry and exit:
>>
>> seccomp_bpf-1307 [000] .... 22974.874393: sys_enter: NR 110 (7ffff22c46e0, 40a350, 4, fffffffffffff7ab, 7fa6ee0d4010, 0)
>> seccomp_bpf-1307 [000] .N.. 22974.874401: sys_exit: NR 110 = 1304
>>
>> Whereas on mainline we see an enter for getpid and an exit for getppid:
>>
>> seccomp_bpf-1030 [000] .... 21.806766: sys_enter: NR 39 (7ffe2f6d1ad0, 40a350, 7ffe2f6d1ad0, 0, 0, 407299)
>> seccomp_bpf-1030 [000] .... 21.806767: sys_exit: NR 110 = 1027
>
> For my own notes, this is how I reproduced it:
>
> # ./perf-$VER record -e raw_syscalls:sys_enter -e raw_syscalls:sys_exit &
> # ./seccomp_bpf
> # fg
> ctrl-c
> # ./perf-$VER script | grep seccomp_bpf | awk '{print $7}' | sort | uniq -c > $VER.log
> *repeat*
> # diff -u old.log new.log
> ...
>
> (Is there an easier way to get those results?)
I did more or less the same thing, except I ran the trace event manually
(via debugfs), which is no better really.
I think the right way to test it would be to have a test that modifies
the syscall via seccomp and also monitors the trace event using perf
events. But that wouldn't be easier :)
> I will go see if I can figure out the best way to correct this.
I think this works?
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 18683598edbc..901361e2f8ea 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -60,13 +60,15 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
return ret;
}
+ syscall = syscall_get_nr(current, regs);
+
if (unlikely(ti_work & _TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, syscall);
syscall_enter_audit(regs, syscall);
/* The above might have changed the syscall number */
- return ret ? : syscall_get_nr(current, regs);
+ return ret ? : syscall;
}
static __always_inline long
cheers
next prev parent reply other threads:[~2020-09-13 7:44 UTC|newest]
Thread overview: 12+ 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
2020-08-21 0:35 ` Thomas Gleixner
2020-08-21 14:21 ` [tip: core/urgent] core/entry: Respect syscall number rewrites tip-bot2 for Thomas Gleixner
[not found] ` <87a6xzrr89.fsf@mpe.ellerman.id.au>
2020-09-11 18:58 ` [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax Kees Cook
2020-09-12 0:10 ` Kees Cook
2020-09-13 7:44 ` Michael Ellerman [this message]
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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