The copy_to_user() here expect can fix the fault on both kernel and
user address, this is not true on other platforms except x86,
change to user copy_in_user() so that can detect the source and
destination address page fault, work as expected:
ENTRY(copy_user_generic_string)
ASM_STAC
cmpl $8,%edx
jb 2f /* less than 8 bytes, go to byte copy loop */
ALIGN_DESTINATION
movl %edx,%ecx
shrl $3,%ecx
andl $7,%edx
1: rep
movsq
2: movl %edx,%ecx
3: rep
movsb
xorl %eax,%eax
ASM_CLAC
ret
.section .fixup,"ax"
11: leal (%rdx,%rcx,8),%ecx
12: movl %ecx,%edx /* ecx is zerorest also */
jmp copy_user_handle_tail
.previous
_ASM_EXTABLE(1b,11b)
_ASM_EXTABLE(3b,12b)
ENDPROC(copy_user_generic_string)
This is the x86 copy_to_user implementation, the fault instruction is
label 1b, 3b, because movsb instruction will fault on both source and
destination address, but on other platforms, like arm64 and arm:
ENTRY(__copy_to_user)
ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \
CONFIG_ARM64_PAN)
add x5, x0, x2 // upper user buffer boundary
subs x2, x2, #16
b.mi 1f
0:
ldp x3, x4, [x1], #16
subs x2, x2, #16
USER(9f, stp x3, x4, [x0], #16)
b.pl 0b
1: adds x2, x2, #8
b.mi 2f
ldr x3, [x1], #8
sub x2, x2, #8
USER(9f, str x3, [x0], #8 )
2: adds x2, x2, #4
b.mi 3f
ldr w3, [x1], #4
sub x2, x2, #4
USER(9f, str w3, [x0], #4 )
3: adds x2, x2, #2
b.mi 4f
ldrh w3, [x1], #2
sub x2, x2, #2
USER(9f, strh w3, [x0], #2 )
4: adds x2, x2, #1
b.mi 5f
ldrb w3, [x1]
USER(9f, strb w3, [x0] )
5: mov x0, #0
It only check the str instructions, means only check fault on destination
address, if the source address in kernel is invalid, it will result in
kernel panic(), this may happened in read_kcore() function, the
kern_addr_valid() only make sure the address is valid during call it,
when it returned, the kernel address may be invalid, like kunmap(),
setfixmap(), vfree() function will change kernel pagetables, and there is
not any sync between read_kcore() and kernel pagetable change. I change
to use copy_in_user(), so that can check both source and destination address,
avoid the kernel panic() in some unlucky circumstance.
Signed-off-by: yalin wang <yalin.wang2...@gmail.com>
---
fs/proc/kcore.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 92e6726..4f28deb 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -515,8 +515,12 @@ read_kcore(struct file *file, char __user *buffer, size_t
buflen, loff_t *fpos)
} else {
if (kern_addr_valid(start)) {
unsigned long n;
-
- n = copy_to_user(buffer, (char *)start, tsz);
+ if ((start + tsz < tsz) ||
+ (start + tsz) > TASK_SIZE)
+ return -EFAULT;
+ set_fs(KERNEL_DS);
+ n = copy_in_user(buffer, (char *)start, tsz);
+ set_fs(USER_DS);
/*
* We cannot distinguish between fault on source
* and fault on destination. When this happens
--
1.9.1
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