path: root/arch
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authorLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 12:56:09 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 12:56:09 -0800
commit594cc251fdd0d231d342d88b2fdff4bc42fb0690 (patch)
tree259269a399e6504a7cf8739201cf172d1cbb197a /arch
parent0b2c8f8b6b0c7530e2866c95862546d0da2057b0 (diff)
make 'user_access_begin()' do 'access_ok()'
Originally, the rule used to be that you'd have to do access_ok() separately, and then user_access_begin() before actually doing the direct (optimized) user access. But experience has shown that people then decide not to do access_ok() at all, and instead rely on it being implied by other operations or similar. Which makes it very hard to verify that the access has actually been range-checked. If you use the unsafe direct user accesses, hardware features (either SMAP - Supervisor Mode Access Protection - on x86, or PAN - Privileged Access Never - on ARM) do force you to use user_access_begin(). But nothing really forces the range check. By putting the range check into user_access_begin(), we actually force people to do the right thing (tm), and the range check vill be visible near the actual accesses. We have way too long a history of people trying to avoid them. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 3920f456db79..a87ab5290ab4 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -705,7 +705,14 @@ extern struct movsl_mask {
* checking before using them, but you have to surround them with the
* user_access_begin/end() pair.
-#define user_access_begin() __uaccess_begin()
+static __must_check inline bool user_access_begin(const void __user *ptr, size_t len)
+ if (unlikely(!access_ok(ptr,len)))
+ return 0;
+ __uaccess_begin();
+ return 1;
+#define user_access_begin(a,b) user_access_begin(a,b)
#define user_access_end() __uaccess_end()
#define unsafe_put_user(x, ptr, err_label) \