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Message-ID: <20240706032005.122654-1-wanglinhui@huawei.com>
Date: Sat, 6 Jul 2024 11:20:05 +0800
From: wanglinhui <wanglinhui@...wei.com>
To: Russell King <linux@...linux.org.uk>, <rmk+kernel@...linux.org.uk>, Andrew
Morton <akpm@...ux-foundation.org>, Kees Cook <kees@...nel.org>, Kefeng Wang
<wangkefeng.wang@...wei.com>, Suren Baghdasaryan <surenb@...gle.com>
CC: Linus Walleij <linus.walleij@...aro.org>, Catalin Marinas
<catalin.marinas@....com>, <linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <wangfangpeng1@...wei.com>,
<zhangxun38@...wei.com>, <yangzhuohao1@...wei.com>
Subject: [PATCH] ARM: Fix "external abort on non-linefetch" kernel panic caused by userspace
0x16800000 is a peripheral physical address that supports only
4-byte-aligned access.
Use /dev/mem to enable the user space to access 0x16800000. Then userspace
unexpectedly tried to read four bytes from 0x16800001 (actually access
its virtual address), which caused the kernel to trigger an
"external abort on non-linefetch" panic:
Unhandled fault: external abort on non-linefetch (0x1018) at 0x0100129b
[0100129b] *pgd=85038831, *pte=16801703, *ppte=16801e33
Internal error: : 1018 [#1] SMP ARM
...
CPU: 2 PID: xxxx Comm: xxxx Tainted: G O 5.10.0 #1
Hardware name: Hisilicon A9
PC is at do_alignment_ldrstr+0xb8/0x100
LR is at 0xc1f203fc
psr: 200f0313
sp : c7081ed4 ip : 00000008 fp : 00000011
r10: b42250c8 r9 : c7081f0c r8 : c7081fb0
r7 : 0100129b r6 : 00000004 r5 : 00000000 r4 : e5908000
r3 : 00000000 r2 : c7081f0c r1 : 200f0210 r0 : 0100129b
Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 1ac5387d Table: 82c3c04a DAC: 55555555
Process LcnNCoreTask (pid: 4049, stack limit = 0x14066b0e)
Call trace:
do_alignment_ldrstr
--do_alignment
----do_DataAbort
------__dabt_usr
It triggers a data abort exception twice. The first time occurs when
an unaligned address is accessed in user mode. The second time occurs
when the peripheral address is actually accessed in kernel mode,
and it crashes the kernel. However, the code location for the second
data abort is as follows:
```
#define __get8_unaligned_check(ins, val, addr, err) \
__asm__(\
ARM("1: "ins" %1, [%2], #1\n") \ <-- Second data abort is triggered here
THUMB("1: "ins" %1, [%2]\n") \
THUMB(" add %2, %2, #1\n") \
"2:\n" \
" .pushsection .text.fixup,\"ax\"\n" \
```
It is an exception table entry that can be fixed up.
There is another test that indicates that
"external abort on non-linefetch" needs to be fixed up.
Similarly, use /dev/mem to map 0x16800000 to the user space.
Pass 0x16800001 (actually passes its virtual address) to the
kernel via the write() system call and write 1 byte.
It also causes the kernel to trigger an
"external abort on non-linefetch" panic:
Unhandled fault: external abort on non-linefetch (0x1018) at 0xb6f95000
[b6f95000] *pgd=83fb6831, *pte=16800783, *ppte=16800e33
Internal error: : 1018 [#1] SMP ARM
...
CPU: 1 PID: xxxx Comm: xxxx Tainted: G O 5.10.0 #1
Hardware name: Hisilicon A9
PC is at __get_user_1+0x14/0x20
LR is at iov_iter_fault_in_readable+0x7c/0x198
psr: 800b0213
sp : c195be18 ip : 00000001 fp : c35a2478
r10: c06b5260 r9 : 00000000 r8 : c356fee0
r7 : ffffe000 r6 : b6f95000 r5 : 00000001 r4 : c195bf10
r3 : b6f95000 r2 : f7f95000 r1 : beffffff r0 : b6f95000
Call trace looks like:
__get_user_1
--iov_iter_fault_in_readable
----generic_perform_write
------__generic_file_write_iter
--------generic_file_write_iter
The location of the instruction that triggers the data abort
is as follows:
```
ENTRY(__get_user_1)
check_uaccess r0, 1, r1, r2, __get_user_bad
1: TUSER(ldrb) r2, [r0] <-- Data abort is triggered here
mov r0, #0
ret lr
ENDPROC(__get_user_1)
_ASM_NOKPROBE(__get_user_1)
```
It is also an exception table entry that can be fixed up.
Address passed in from user space should not crash the kernel.
Therefore, fixup_exception() is added to fix up such exception.
Fixes: 136848d4ca9c ("ARM: LPAE: Move the FSR definitions to separate files")
Signed-off-by: wanglinhui <wanglinhui@...wei.com>
---
arch/arm/mm/fault.c | 9 +++++++++
arch/arm/mm/fsr-2level.c | 4 ++--
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 67c425341a95..55776dcde015 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -558,6 +558,15 @@ do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
return 1;
}
+static int do_fixup_exception(unsigned long addr, unsigned int fsr,
+ struct pt_regs *regs)
+{
+ if (fixup_exception(regs))
+ return 0;
+
+ return 1;
+}
+
struct fsr_info {
int (*fn)(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
int sig;
diff --git a/arch/arm/mm/fsr-2level.c b/arch/arm/mm/fsr-2level.c
index f2be95197265..a80444db9b3e 100644
--- a/arch/arm/mm/fsr-2level.c
+++ b/arch/arm/mm/fsr-2level.c
@@ -12,9 +12,9 @@ static struct fsr_info fsr_info[] = {
{ do_translation_fault, SIGSEGV, SEGV_MAPERR, "section translation fault" },
{ do_bad, SIGBUS, 0, "external abort on linefetch" },
{ do_page_fault, SIGSEGV, SEGV_MAPERR, "page translation fault" },
- { do_bad, SIGBUS, 0, "external abort on non-linefetch" },
+ { do_fixup_exception, SIGBUS, 0, "external abort on non-linefetch" },
{ do_bad, SIGSEGV, SEGV_ACCERR, "section domain fault" },
- { do_bad, SIGBUS, 0, "external abort on non-linefetch" },
+ { do_fixup_exception, SIGBUS, 0, "external abort on non-linefetch" },
{ do_bad, SIGSEGV, SEGV_ACCERR, "page domain fault" },
{ do_bad, SIGBUS, 0, "external abort on translation" },
{ do_sect_fault, SIGSEGV, SEGV_ACCERR, "section permission fault" },
--
2.12.3
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