Hi,
Le 02/09/2024 à 07:31, Omar Sandoval a écrit :
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From: Omar Sandoval <osandov@xxxxxx>
I found that on x86, copy_to_kernel_nofault() still faults on addresses
outside of the kernel address range (including NULL):
# echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
# echo g > /proc/sysrq-trigger
...
[15]kdb> mm 0 1234
[ 94.652476] BUG: kernel NULL pointer dereference, address: 0000000000000000
...
Note that copy_to_kernel_nofault() uses pagefault_disable(), but it
still faults. This is because with Supervisor Mode Access Prevention
(SMAP) enabled, do_user_addr_fault() Oopses on a fault for a user
address from kernel space _before_ checking faulthandler_disabled().
copy_from_kernel_nofault() avoids this by checking that the address is
in the kernel before doing the actual memory access. Do the same in
copy_to_kernel_nofault() so that we get an error as expected:
# echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
# echo g > /proc/sysrq-trigger
...
[17]kdb> mm 0 1234
kdb_putarea_size: Bad address 0x0
diag: -21: Invalid address
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
mm/maccess.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/maccess.c b/mm/maccess.c
index 72e9c03ea37f..d67dee51a1cc 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -61,6 +61,9 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
align = (unsigned long)dst | (unsigned long)src;
+ if (!copy_kernel_nofault_allowed(dst, size))
+ return -ERANGE;
+
pagefault_disable();
if (!(align & 7))
copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
--
2.46.0
This patch leads to the following errors on ppc64le_defconfig:
[ 2.423930][ T1] Running code patching self-tests ...
[ 2.428912][ T1] code-patching: test failed at line 395
[ 2.429085][ T1] code-patching: test failed at line 398
[ 2.429561][ T1] code-patching: test failed at line 432
[ 2.429679][ T1] code-patching: test failed at line 435
This seems to be linked to commit c28c15b6d28a ("powerpc/code-patching:
Use temporary mm for Radix MMU"), copy_from_kernel_nofault_allowed()
returns false for the patching area.
Christophe
