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>
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- arch/x86/include/asm/uaccess.h 8 additions, 1 deletionarch/x86/include/asm/uaccess.h
- drivers/gpu/drm/i915/i915_gem_execbuffer.c 13 additions, 2 deletionsdrivers/gpu/drm/i915/i915_gem_execbuffer.c
- include/linux/uaccess.h 1 addition, 1 deletioninclude/linux/uaccess.h
- kernel/compat.c 2 additions, 4 deletionskernel/compat.c
- kernel/exit.c 2 additions, 4 deletionskernel/exit.c
- lib/strncpy_from_user.c 5 additions, 4 deletionslib/strncpy_from_user.c
- lib/strnlen_user.c 5 additions, 4 deletionslib/strnlen_user.c
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