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authorJiri Olsa <jolsa@redhat.com>2011-05-12 16:30:30 +0200
committerIngo Molnar <mingo@elte.hu>2011-05-18 12:49:00 +0200
commit26afb7c661080ae3f1f13ddf7f0c58c4f931c22b (patch)
treef3774d2514c92ad2efaaaa9da3f10c140762ca5d /arch/x86/lib
parent2f19e06ac30771c7cb96fd61d8aeacfa74dac21c (diff)
x86, 64-bit: Fix copy_[to/from]_user() checks for the userspace address limit
As reported in BZ #30352: https://bugzilla.kernel.org/show_bug.cgi?id=30352 there's a kernel bug related to reading the last allowed page on x86_64. The _copy_to_user() and _copy_from_user() functions use the following check for address limit: if (buf + size >= limit) fail(); while it should be more permissive: if (buf + size > limit) fail(); That's because the size represents the number of bytes being read/write from/to buf address AND including the buf address. So the copy function will actually never touch the limit address even if "buf + size == limit". Following program fails to use the last page as buffer due to the wrong limit check: #include <sys/mman.h> #include <sys/socket.h> #include <assert.h> #define PAGE_SIZE (4096) #define LAST_PAGE ((void*)(0x7fffffffe000)) int main() { int fds[2], err; void * ptr = mmap(LAST_PAGE, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0); assert(ptr == LAST_PAGE); err = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds); assert(err == 0); err = send(fds[0], ptr, PAGE_SIZE, 0); perror("send"); assert(err == PAGE_SIZE); err = recv(fds[1], ptr, PAGE_SIZE, MSG_WAITALL); perror("recv"); assert(err == PAGE_SIZE); return 0; } The other place checking the addr limit is the access_ok() function, which is working properly. There's just a misleading comment for the __range_not_ok() macro - which this patch fixes as well. The last page of the user-space address range is a guard page and Brian Gerst observed that the guard page itself due to an erratum on K8 cpus (#121 Sequential Execution Across Non-Canonical Boundary Causes Processor Hang). However, the test code is using the last valid page before the guard page. The bug is that the last byte before the guard page can't be read because of the off-by-one error. The guard page is left in place. This bug would normally not show up because the last page is part of the process stack and never accessed via syscalls. Signed-off-by: Jiri Olsa <jolsa@redhat.com> Acked-by: Brian Gerst <brgerst@gmail.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: <stable@kernel.org> Link: http://lkml.kernel.org/r/1305210630-7136-1-git-send-email-jolsa@redhat.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/copy_user_64.S4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index d17a1170bbf5..024840266ba0 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -79,7 +79,7 @@ ENTRY(_copy_to_user)
addq %rdx,%rcx
jc bad_to_user
cmpq TI_addr_limit(%rax),%rcx
- jae bad_to_user
+ ja bad_to_user
ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,X86_FEATURE_ERMS, \
copy_user_generic_unrolled,copy_user_generic_string, \
copy_user_enhanced_fast_string
@@ -94,7 +94,7 @@ ENTRY(_copy_from_user)
addq %rdx,%rcx
jc bad_from_user
cmpq TI_addr_limit(%rax),%rcx
- jae bad_from_user
+ ja bad_from_user
ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,X86_FEATURE_ERMS, \
copy_user_generic_unrolled,copy_user_generic_string, \
copy_user_enhanced_fast_string