From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Huckleberry <nhuck15@gmail.com>,
Russell King <linux@armlinux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Chunyan Zhang <zhang.lyra@gmail.com>,
clang-built-linux@googlegroups.com,
Dmitry Safonov <0x7f454c46@gmail.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org,
Lvqiang Huang <lvqiang.huang@unisoc.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Miles Chen <miles.chen@mediatek.com>,
stable@vger.kernel.org
Subject: [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference
Date: Thu, 30 Jul 2020 13:51:10 -0700 [thread overview]
Message-ID: <20200730205112.2099429-3-ndesaulniers@google.com> (raw)
In-Reply-To: <20200730205112.2099429-1-ndesaulniers@google.com>
If the value of the link register is not correct (tail call from asm
that didn't set it, stack corruption, memory no longer mapped), then
using it for an address calculation may trigger an exception. Without a
fixup handler, this will lead to a panic, which will unwind, which will
trigger the fault repeatedly in an infinite loop.
We don't observe such failures currently, but we have. Just to be safe,
add a fixup handler here so that at least we don't have an infinite
loop.
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 | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S
index 5388ac664c12..40eb2215eaf4 100644
--- a/arch/arm/lib/backtrace-clang.S
+++ b/arch/arm/lib/backtrace-clang.S
@@ -146,7 +146,7 @@ for_each_frame: tst frame, mask @ Check for address exceptions
tst sv_lr, #0 @ If there's no previous lr,
beq finished_setup @ we're done.
- ldr r0, [sv_lr, #-4] @ get call instruction
+prev_call: ldr r0, [sv_lr, #-4] @ get call instruction
ldr r3, .Lopcode+4
and r2, r3, r0 @ is this a bl call
teq r2, r3
@@ -206,6 +206,13 @@ finished_setup:
mov r2, frame
bl printk
no_frame: ldmfd sp!, {r4 - r9, fp, pc}
+/*
+ * Accessing the address pointed to by the link register triggered an
+ * exception, don't try to unwind through it.
+ */
+bad_lr: mov sv_fp, #0
+ mov sv_lr, #0
+ b finished_setup
ENDPROC(c_backtrace)
.pushsection __ex_table,"a"
.align 3
@@ -214,6 +221,7 @@ ENDPROC(c_backtrace)
.long 1003b, 1006b
.long 1004b, 1006b
.long 1005b, 1006b
+ .long prev_call, bad_lr
.popsection
.Lbad: .asciz "%sBacktrace aborted due to bad frame pointer <%p>\n"
--
2.28.0.163.g6104cc2f0b6-goog
next prev parent reply other threads:[~2020-07-30 20:51 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
2020-07-30 20:51 ` Nick Desaulniers [this message]
2020-08-06 22:38 ` [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200730205112.2099429-3-ndesaulniers@google.com \
--to=ndesaulniers@google.com \
--cc=0x7f454c46@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=clang-built-linux@googlegroups.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mediatek@lists.infradead.org \
--cc=linux@armlinux.org.uk \
--cc=lvqiang.huang@unisoc.com \
--cc=matthias.bgg@gmail.com \
--cc=miles.chen@mediatek.com \
--cc=nhuck15@gmail.com \
--cc=stable@vger.kernel.org \
--cc=zhang.lyra@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).