From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Luis Machado <luis.machado@linaro.org>,
catalin.marinas@arm.com, Keno Fischer <keno@juliacomputing.com>,
kernel-team@android.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 6/7] arm64: ptrace: Use NO_SYSCALL instead of -1 in syscall_trace_enter()
Date: Sun, 12 Jul 2020 19:32:13 -0700 [thread overview]
Message-ID: <202007121931.A31FBE6@keescook> (raw)
In-Reply-To: <20200710161148.GC31036@willie-the-truck>
On Fri, Jul 10, 2020 at 05:11:48PM +0100, Will Deacon wrote:
> On Fri, Jul 10, 2020 at 09:04:08AM -0700, Kees Cook wrote:
> > On Fri, Jul 10, 2020 at 02:07:01PM +0100, Will Deacon wrote:
> > > Setting a system call number of -1 is special, as it indicates that the
> > > current system call should be skipped.
> > >
> > > Use NO_SYSCALL instead of -1 when checking for this scenario, which is
> > > different from the -1 returned due to a seccomp failure.
> >
> > I can't understand this paragraph. NO_SYSCALL is -1, so how is this
> > "different"?
> >
> > arch/arm64/include/asm/ptrace.h:#define NO_SYSCALL (-1)
> >
> > Do you just mean "stop using a literal '-1'"?
>
> Yes, I'm trying to distinguish '-1' when used as a system call number
> from '-1' when used as the return value of secure_computing() on failure.
> It's currently all mixed up, and I think it's confusing trying to realise
> what is a system call number and what is an error code.
Okay, I gotcha now. Yes, that's entirely reasonable. (It's perhaps an
artifact of x86's implementation that they get directly passed through.)
--
Kees Cook
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next prev parent reply other threads:[~2020-07-13 2:33 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-10 13:06 [PATCH v3 0/7] arm64: Fix single-step handling and syscall tracing Will Deacon
2020-07-10 13:06 ` [PATCH v3 1/7] arm64: ptrace: Consistently use pseudo-singlestep exceptions Will Deacon
2020-07-16 0:27 ` Sasha Levin
2020-07-10 13:06 ` [PATCH v3 2/7] arm64: ptrace: Override SPSR.SS when single-stepping is enabled Will Deacon
2020-07-16 0:27 ` Sasha Levin
2020-07-10 13:06 ` [PATCH v3 3/7] arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return Will Deacon
2020-07-16 0:27 ` Sasha Levin
2020-07-10 13:06 ` [PATCH v3 4/7] arm64: ptrace: Add a comment describing our syscall entry/exit trap ABI Will Deacon
2020-07-10 13:07 ` [PATCH v3 5/7] arm64: syscall: Expand the comment about ptrace and syscall(-1) Will Deacon
2020-07-10 13:07 ` [PATCH v3 6/7] arm64: ptrace: Use NO_SYSCALL instead of -1 in syscall_trace_enter() Will Deacon
2020-07-10 16:04 ` Kees Cook
2020-07-10 16:11 ` Will Deacon
2020-07-13 2:32 ` Kees Cook [this message]
2020-07-10 13:07 ` [PATCH v3 7/7] arm64: Use test_tsk_thread_flag() for checking TIF_SINGLESTEP Will Deacon
2020-07-14 11:57 ` [PATCH v3 0/7] arm64: Fix single-step handling and syscall tracing Luis Machado
2020-07-15 12:25 ` Luis Machado
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