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Subject[PATCH v3 6/6] ARM: mm: Fix PXN process with LPAE feature
Date
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"

As Permission fault shows in ARM spec,
IFSR format when using the Short-descriptor translation table format
Permission fault: 01101 First level 01111 Second level
IFSR format when using the Long-descriptor translation table format
Permission fault: 0011LL LL bits indicate levelb.

Add is_permission_fault() function to check permission fault and die
if permission fault occurred under instruction fault in do_page_fault().

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 | 20 +++++++++++++++++++-
arch/arm/mm/fault.h | 4 ++++
2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 82bcfe57de20..bc8779d54a64 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -194,6 +194,19 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
#define VM_FAULT_BADMAP 0x010000
#define VM_FAULT_BADACCESS 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)
@@ -253,9 +266,14 @@ 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;

+ if (is_permission_fault(fsr) && !user_mode(regs))
+ die_kernel_fault("execution of memory",
+ mm, addr, fsr, regs);
+ }
+
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

/*
diff --git a/arch/arm/mm/fault.h b/arch/arm/mm/fault.h
index 9ecc2097a87a..83b5ab32d7a4 100644
--- a/arch/arm/mm/fault.h
+++ b/arch/arm/mm/fault.h
@@ -14,6 +14,8 @@

#ifdef CONFIG_ARM_LPAE
#define FSR_FS_AEA 17
+#define FS_PERM_NOLL 0xC
+#define FS_PERM_NOLL_MASK 0x3C

static inline int fsr_fs(unsigned int fsr)
{
@@ -21,6 +23,8 @@ static inline int fsr_fs(unsigned int fsr)
}
#else
#define FSR_FS_AEA 22
+#define FS_L1_PERM 0xD
+#define FS_L2_PERM 0xF

static inline int fsr_fs(unsigned int fsr)
{
--
2.26.2
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