[PATCH v2] ARM: mm: Provide better fault message for permission fault

Kefeng Wang
2022-09-19T10:47:48Z

If there is a permission fault in __do_kernel_fault(), we only
print the generic "paging request" message which don't show
read, write or excute information, let's provide better fault
message for them.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
v2: fix !CONFIG_MMU built

arch/arm/mm/fault.c | 35 +++++++++++++++++++++--------------
1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 46cccd6bf705..387c87112d80 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -105,6 +105,19 @@ static inline bool is_write_fault(unsigned int fsr)
return (fsr & FSR_WRITE) && !(fsr & FSR_CM);
}

+static inline bool is_permission_fault(unsigned int fsr)
+{
+ int fs = fsr_fs(fsr);
+#ifdef CONFIG_ARM_LPAE
+ if ((fs & FS_PERM_NOLL_MASK) == FS_PERM_NOLL)
+ return true;
+#else
+ if (fs == FS_L1_PERM || fs == FS_L2_PERM)
+ return true;
+#endif
+ return false;
+}
+
static void die_kernel_fault(const char *msg, struct mm_struct *mm,
unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
@@ -137,7 +150,14 @@ __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
/*
* No handler, we'll have to terminate things with extreme prejudice.
*/
- if (addr < PAGE_SIZE) {
+ if (is_permission_fault(fsr)) {
+ if (fsr & FSR_WRITE)
+ msg = "write to read-only memory";
+ else if (fsr & FSR_LNX_PF)
+ msg = "execute from non-executable memory";
+ else
+ msg = "read from unreadable memory";
+ } else if (addr < PAGE_SIZE) {
msg = "NULL pointer dereference";
} else {
if (kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
@@ -204,19 +224,6 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
#define VM_FAULT_BADMAP ((__force vm_fault_t)0x010000)
#define VM_FAULT_BADACCESS ((__force vm_fault_t)0x020000)

-static inline bool is_permission_fault(unsigned int fsr)
-{
- int fs = fsr_fs(fsr);
-#ifdef CONFIG_ARM_LPAE
- if ((fs & FS_PERM_NOLL_MASK) == FS_PERM_NOLL)
- return true;
-#else
- if (fs == FS_L1_PERM || fs == FS_L2_PERM)
- return true;
-#endif
- return false;
-}
-
static vm_fault_t __kprobes
__do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int flags,
unsigned long vma_flags, struct pt_regs *regs)
--
2.35.3