From 1492c6b1874ac5ed57d8ffef89e2b5c59f804aa8 Mon Sep 17 00:00:00 2001 From: Henry Willard Date: Wed, 12 Apr 2023 15:29:53 -0600 Subject: [PATCH] MIPS: Don't clear _PAGE_SPECIAL in _PAGE_CHG_MASK In the special case where p = mmap(NULL, ALLOC_SIZE, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0); is followed by rc = mprotect(p, ALLOC_SIZE, PROT_NONE); the _PAGE_SPECIAL bit in the page tables will be cleared by mistake and the later unmapped operations will incorrectly modify the struct page for the the zero page. This sequence occurs in the madvise05 test of the Linux Test Project suite of tests. This was discovered while testing an older version of the kernel (5.4.17) on a MIPS device. Unfortunately, support for this device is not available in newer kernels, so I can't test this with the latest Linux kernel code. It looks like the problem exists in newer kernels, but I can't verify it. Except for the LTP test, this sequence of calls is probably not common. Passing it along in the hope it will be useful to someone. Signed-off-by: Henry Willard Signed-off-by: Thomas Bogendoerfer --- arch/mips/include/asm/pgtable-bits.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/mips/include/asm/pgtable-bits.h b/arch/mips/include/asm/pgtable-bits.h index 2362842..1c57667 100644 --- a/arch/mips/include/asm/pgtable-bits.h +++ b/arch/mips/include/asm/pgtable-bits.h @@ -280,6 +280,7 @@ static inline uint64_t pte_to_entrylo(unsigned long pte_val) #define __WRITEABLE (_PAGE_SILENT_WRITE | _PAGE_WRITE | _PAGE_MODIFIED) #define _PAGE_CHG_MASK (_PAGE_ACCESSED | _PAGE_MODIFIED | \ - _PAGE_SOFT_DIRTY | _PFN_MASK | _CACHE_MASK) + _PAGE_SOFT_DIRTY | _PFN_MASK | \ + _CACHE_MASK | _PAGE_SPECIAL) #endif /* _ASM_PGTABLE_BITS_H */ -- 2.7.4