From 4ecf886045152d2ddf98ae74e39f789868ac1f98 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 11 Feb 2015 15:25:35 -0800 Subject: [PATCH] sparc32: fix broken set_pte() 32-bit sparc uses swap instruction to implement set_pte(). It called using GCC inline assembler. But it misses the "memory" clobber to indicate that pte value will be updated in memory. As result GCC doesn't know that it cannot postpone pte pointer dereference which occurs before set_pte() to post-set_pte() time. It leads to real-world bugs -- [1]. In this situation we have code: ptent = ptep_modify_prot_start(mm, addr, pte); ptent = pte_modify(ptent, newprot); ... ptep_modify_prot_commit(mm, addr, pte, ptent); ptep_modify_prot_start() in sparc case is just 'pte' dereference plus pte_clear(). pte_clear() calls broken set_pte(). GCC thinks it's valid to dereference 'pte' again on pte_modify() and gets cleared pte. ptep_modify_prot_commit() puts 'pteent' with pfn==0 back to page table, which eventually leads to the crash. [1] http://lkml.kernel.org/r/54C06B19.8060305@roeck-us.net Signed-off-by: Kirill A. Shutemov Reported-by: Guenter Roeck Tested-by: Guenter Roeck Cc: Paul Moore Cc: Joonsoo Kim Cc: David Miller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/sparc/include/asm/pgtable_32.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/sparc/include/asm/pgtable_32.h b/arch/sparc/include/asm/pgtable_32.h index b2f7dc46a7d1..9912eb0b499a 100644 --- a/arch/sparc/include/asm/pgtable_32.h +++ b/arch/sparc/include/asm/pgtable_32.h @@ -102,7 +102,8 @@ extern unsigned long empty_zero_page; */ static inline unsigned long srmmu_swap(unsigned long *addr, unsigned long value) { - __asm__ __volatile__("swap [%2], %0" : "=&r" (value) : "0" (value), "r" (addr)); + __asm__ __volatile__("swap [%2], %0" : + "=&r" (value) : "0" (value), "r" (addr) : "memory"); return value; } -- 2.20.1