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Message-Id: <1190fd24-7d6a-4f6a-a3e3-ba3564c2303c@app.fastmail.com>
Date: Thu, 10 Aug 2023 22:17:45 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Kees Cook" <keescook@...omium.org>,
"Russell King" <linux@...linux.org.uk>
Cc: "Arnd Bergmann" <arnd@...nel.org>,
"Lecopzer Chen" <lecopzer.chen@...iatek.com>,
"Oleg Nesterov" <oleg@...hat.com>,
linux-arm-kernel@...ts.infradead.org,
"Matthias Brugger" <matthias.bgg@...il.com>,
"AngeloGioacchino Del Regno"
<angelogioacchino.delregno@...labora.com>,
"Linus Walleij" <linus.walleij@...aro.org>,
"Wolfram Sang" <wsa@...nel.org>,
"Dan Williams" <dan.j.williams@...el.com>,
"Russell King" <rmk+kernel@...linux.org.uk>,
linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ARM: ptrace: Restore syscall restart tracing
On Thu, Aug 10, 2023, at 21:54, Kees Cook wrote:
> Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store
> thread_info->abi_syscall"), the seccomp selftests "syscall_restart" has
> been broken. This was caused by the restart syscall not being stored to
> "abi_syscall" during restart setup before branching to the "local_restart"
> label. Tracers would see the wrong syscall, and scno would get overwritten
> while returning from the TIF_WORK path. Add the missing store.
>
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index bcc4c9ec3aa4..5c31e9de7a60 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -90,6 +90,7 @@ slow_work_pending:
> cmp r0, #0
> beq no_work_pending
> movlt scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE)
> + str scno, [tsk, #TI_ABI_SYSCALL] @ make sure tracers see update
> ldmia sp, {r0 - r6} @ have to reload r0 - r6
> b local_restart @ ... and off we go
> ENDPROC(ret_fast_syscall)
Looks good to me, as in my previous reply this is safe for all cases
with the current restartable syscalls, though it would be wrong if
we had a restartblock version of epoll_wait on an OABI_COMPAT task,
which needs to look at the high bits of the number to tell which
structure layout to use.
I also looked at my original patch now and see what I did wrong
there.
Reviewed-by: Arnd Bergmann <arnd@...db.de>
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