From 9063c61fd5cbd6f42e95929aa0e02380c9e15656 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 20 Jun 2009 15:40:00 -0700 Subject: [PATCH] x86, 64-bit: Clean up user address masking The discussion about using "access_ok()" in get_user_pages_fast() (see commit 7f8189068726492950bf1a2dcfd9b51314560abf: "x86: don't use 'access_ok()' as a range check in get_user_pages_fast()" for details and end result), made us notice that x86-64 was really being very sloppy about virtual address checking. So be way more careful and straightforward about masking x86-64 virtual addresses: - All the VIRTUAL_MASK* variants now cover half of the address space, it's not like we can use the full mask on a signed integer, and the larger mask just invites mistakes when applying it to either half of the 48-bit address space. - /proc/kcore's kc_offset_to_vaddr() becomes a lot more obvious when it transforms a file offset into a (kernel-half) virtual address. - Unify/simplify the 32-bit and 64-bit USER_DS definition to be based on TASK_SIZE_MAX. This cleanup and more careful/obvious user virtual address checking also uncovered a buglet in the x86-64 implementation of strnlen_user(): it would do an "access_ok()" check on the whole potential area, even if the string itself was much shorter, and thus return an error even for valid strings. Our sloppy checking had hidden this. So this fixes 'strnlen_user()' to do this properly, the same way we already handled user strings in 'strncpy_from_user()'. Namely by just checking the first byte, and then relying on fault handling for the rest. That always works, since we impose a guard page that cannot be mapped at the end of the user space address space (and even if we didn't, we'd have the address space hole). Acked-by: Ingo Molnar Cc: Peter Zijlstra Cc: Andrew Morton Cc: Nick Piggin Cc: Hugh Dickins Cc: H. Peter Anvin Cc: Thomas Gleixner Cc: Alan Cox Signed-off-by: Linus Torvalds --- arch/x86/include/asm/page_64_types.h | 2 +- arch/x86/include/asm/pgtable_64.h | 5 +---- arch/x86/include/asm/uaccess.h | 7 +------ arch/x86/lib/usercopy_64.c | 2 +- 4 files changed, 4 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h index 8d382d3abf3..7639dbf5d22 100644 --- a/arch/x86/include/asm/page_64_types.h +++ b/arch/x86/include/asm/page_64_types.h @@ -41,7 +41,7 @@ /* See Documentation/x86/x86_64/mm.txt for a description of the memory map. */ #define __PHYSICAL_MASK_SHIFT 46 -#define __VIRTUAL_MASK_SHIFT 48 +#define __VIRTUAL_MASK_SHIFT 47 /* * Kernel image size is limited to 512 MB (see level2_kernel_pgt in diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h index abde308fdb0..c57a3011714 100644 --- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -165,10 +165,7 @@ extern void cleanup_highmap(void); /* fs/proc/kcore.c */ #define kc_vaddr_to_offset(v) ((v) & __VIRTUAL_MASK) -#define kc_offset_to_vaddr(o) \ - (((o) & (1UL << (__VIRTUAL_MASK_SHIFT - 1))) \ - ? ((o) | ~__VIRTUAL_MASK) \ - : (o)) +#define kc_offset_to_vaddr(o) ((o) | ~__VIRTUAL_MASK) #define __HAVE_ARCH_PTE_SAME #endif /* !__ASSEMBLY__ */ diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 512ee87062c..20e6a795e16 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -25,12 +25,7 @@ #define MAKE_MM_SEG(s) ((mm_segment_t) { (s) }) #define KERNEL_DS MAKE_MM_SEG(-1UL) - -#ifdef CONFIG_X86_32 -# define USER_DS MAKE_MM_SEG(PAGE_OFFSET) -#else -# define USER_DS MAKE_MM_SEG(__VIRTUAL_MASK) -#endif +#define USER_DS MAKE_MM_SEG(TASK_SIZE_MAX) #define get_ds() (KERNEL_DS) #define get_fs() (current_thread_info()->addr_limit) diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index ec13cb5f17e..b7c2849ffb6 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -127,7 +127,7 @@ EXPORT_SYMBOL(__strnlen_user); long strnlen_user(const char __user *s, long n) { - if (!access_ok(VERIFY_READ, s, n)) + if (!access_ok(VERIFY_READ, s, 1)) return 0; return __strnlen_user(s, n); } -- 2.20.1