[PATCH v2 7/7] ARM: mm: Fix PXN process with LPAE feature

Kefeng Wang
2021-06-02T06:53:54Z

When user code execution with privilege mode, it will lead to
infinite loop in the page fault handler if ARM_LPAE enabled,

The issue could be reproduced with
"echo EXEC_USERSPACE > /sys/kernel/debug/provoke-crash/DIRECT"

Lets' fix it by adding the check in do_page_fault() and panic
when ARM_LPAE enabled.

Fixes: 1d4d37159d01 ("ARM: 8235/1: Support for the PXN CPU feature on ARMv7")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
arch/arm/mm/fault.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 7cfa9a59d3ec..279bbeb33b48 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -257,8 +257,14 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
vm_flags = VM_WRITE;
}

- if (fsr & FSR_LNX_PF)
+ if (fsr & FSR_LNX_PF) {
vm_flags = VM_EXEC;
+#ifdef CONFIG_ARM_LPAE
+ if (addr && addr < TASK_SIZE && !user_mode(regs))
+ die_kernel_fault("execution of user memory",
+ addr, fsr, regs);
+#endif
+ }

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

--
2.26.2