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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 1/4] ARM: backtrace-clang: check for NULL lr
Date: Thu, 30 Jul 2020 13:51:09 -0700	[thread overview]
Message-ID: <20200730205112.2099429-2-ndesaulniers@google.com> (raw)
In-Reply-To: <20200730205112.2099429-1-ndesaulniers@google.com>

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


WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Huckleberry <nhuck15@gmail.com>,
	Russell King <linux@armlinux.org.uk>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	linux-kernel@vger.kernel.org, stable@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: [PATCH 1/4] ARM: backtrace-clang: check for NULL lr
Date: Thu, 30 Jul 2020 13:51:09 -0700	[thread overview]
Message-ID: <20200730205112.2099429-2-ndesaulniers@google.com> (raw)
In-Reply-To: <20200730205112.2099429-1-ndesaulniers@google.com>

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


_______________________________________________
Linux-mediatek mailing list
Linux-mediatek@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-mediatek

WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Huckleberry <nhuck15@gmail.com>,
	Russell King <linux@armlinux.org.uk>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	linux-kernel@vger.kernel.org, stable@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: [PATCH 1/4] ARM: backtrace-clang: check for NULL lr
Date: Thu, 30 Jul 2020 13:51:09 -0700	[thread overview]
Message-ID: <20200730205112.2099429-2-ndesaulniers@google.com> (raw)
In-Reply-To: <20200730205112.2099429-1-ndesaulniers@google.com>

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


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-07-30 20:51 UTC|newest]

Thread overview: 40+ 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 ` Nick Desaulniers
2020-07-30 20:51 ` Nick Desaulniers
2020-07-30 20:51 ` Nick Desaulniers [this message]
2020-07-30 20:51   ` [PATCH 1/4] ARM: backtrace-clang: check for NULL lr Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-08-07 18:07   ` Nathan Huckleberry
2020-08-07 18:07     ` Nathan Huckleberry
2020-08-07 18:07     ` Nathan Huckleberry
2020-07-30 20:51 ` [PATCH 2/4] ARM: backtrace-clang: add fixup for lr dereference Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-08-01 23:18   ` Sasha Levin
2020-08-03 18:13     ` Nick Desaulniers
2020-08-04  6:27       ` Greg KH
2020-08-06  1:24   ` Sasha Levin
2020-08-06 22:38   ` Nathan Huckleberry
2020-08-06 22:38     ` Nathan Huckleberry
2020-08-06 22:38     ` Nathan Huckleberry
2020-08-10 22:33     ` Nick Desaulniers
2020-08-10 22:33       ` Nick Desaulniers
2020-08-10 22:33       ` Nick Desaulniers
2020-08-20  0:13       ` Nick Desaulniers
2020-08-20  0:13         ` Nick Desaulniers
2020-08-20  0:13         ` Nick Desaulniers
2020-08-13 16:25   ` Sasha Levin
2020-08-19 23:56   ` Sasha Levin
2020-07-30 20:51 ` [PATCH 3/4] ARM: backtrace-clang: give labels more descriptive names Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-08-06 22:39   ` Nathan Huckleberry
2020-08-06 22:39     ` Nathan Huckleberry
2020-08-06 22:39     ` Nathan Huckleberry
2020-08-10 22:32     ` Nick Desaulniers
2020-08-10 22:32       ` Nick Desaulniers
2020-08-10 22:32       ` Nick Desaulniers
2020-07-30 20:51 ` [PATCH 4/4] ARM: backtrace: use more descriptive labels Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-07-30 20:51   ` Nick Desaulniers
2020-08-06  1:24 ` [PATCH 0/4] CONFIG_UNWINDER_FRAME_POINTER fixes+cleanups Sasha Levin

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