From: Nathan Huckleberry <nhuck15@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>,
Dmitry Safonov <0x7f454c46@gmail.com>,
Russell King <linux@armlinux.org.uk>,
stable@vger.kernel.org, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com,
Miles Chen <miles.chen@mediatek.com>,
linux-mediatek@lists.infradead.org,
Matthias Brugger <matthias.bgg@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Lvqiang Huang <lvqiang.huang@unisoc.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/4] ARM: backtrace-clang: check for NULL lr
Date: Fri, 7 Aug 2020 13:07:21 -0500 [thread overview]
Message-ID: <CAN=-RxtoXCG5h2qirsrLG2P37pjjMEHgfAv-7+NSVUy9_LPaYQ@mail.gmail.com> (raw)
In-Reply-To: <20200730205112.2099429-2-ndesaulniers@google.com>
On Thu, Jul 30, 2020 at 3:51 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> If the link register was zeroed out, do not attempt to use it for
> address calculations for which there are currently no fixup handlers,
> which can lead to a panic during unwind. Since panicking triggers
> another unwind, this can lead to an infinite loop. If this occurs
> during start_kernel(), this can prevent a kernel from booting.
>
> commit 59b6359dd92d ("ARM: 8702/1: head-common.S: Clear lr before jumping to start_kernel()")
> intentionally zeros out the link register in __mmap_switched which tail
> calls into start kernel. Test for this condition so that we can stop
> unwinding when initiated within start_kernel() correctly.
>
> Cc: stable@vger.kernel.org
> Fixes: commit 6dc5fd93b2f1 ("ARM: 8900/1: UNWINDER_FRAME_POINTER implementation for Clang")
> Reported-by: Miles Chen <miles.chen@mediatek.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> arch/arm/lib/backtrace-clang.S | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S
> index 6174c45f53a5..5388ac664c12 100644
> --- a/arch/arm/lib/backtrace-clang.S
> +++ b/arch/arm/lib/backtrace-clang.S
> @@ -144,6 +144,8 @@ for_each_frame: tst frame, mask @ Check for address exceptions
> */
> 1003: ldr sv_lr, [sv_fp, #4] @ get saved lr from next frame
>
> + tst sv_lr, #0 @ If there's no previous lr,
> + beq finished_setup @ we're done.
> ldr r0, [sv_lr, #-4] @ get call instruction
> ldr r3, .Lopcode+4
> and r2, r3, r0 @ is this a bl call
> --
> 2.28.0.163.g6104cc2f0b6-goog
>
Reviewed-by: Nathan Huckleberry <nhuck15@gmail.com>
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next prev parent reply other threads:[~2020-08-07 18:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 20:51 [PATCH 0/4] CONFIG_UNWINDER_FRAME_POINTER fixes+cleanups Nick Desaulniers
2020-07-30 20:51 ` [PATCH 1/4] ARM: backtrace-clang: check for NULL lr Nick Desaulniers
2020-08-07 18:07 ` Nathan Huckleberry [this message]
2020-07-30 20:51 ` [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference Nick Desaulniers
2020-08-06 22:38 ` Nathan Huckleberry
2020-08-10 22:33 ` Nick Desaulniers
2020-08-20 0:13 ` Nick Desaulniers
2020-07-30 20:51 ` [PATCH 3/4] ARM: backtrace-clang: give labels more descriptive names Nick Desaulniers
2020-08-06 22:39 ` Nathan Huckleberry
2020-08-10 22:32 ` Nick Desaulniers
2020-07-30 20:51 ` [PATCH 4/4] ARM: backtrace: use more descriptive labels Nick Desaulniers
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