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

[Kefeng Wang]

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@xxxxxxxxxx>
---
 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