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304ec1b050
Quoting Linus:
I do think that it would be a good idea to very expressly document
the fact that it's not that the user access itself is unsafe. I do
agree that things like "get_user()" want to be protected, but not
because of any direct bugs or problems with get_user() and friends,
but simply because get_user() is an excellent source of a pointer
that is obviously controlled from a potentially attacking user
space. So it's a prime candidate for then finding _subsequent_
accesses that can then be used to perturb the cache.
__uaccess_begin_nospec() covers __get_user() and copy_from_iter() where the
limit check is far away from the user pointer de-reference. In those cases
a barrier_nospec() prevents speculation with a potential pointer to
privileged memory. uaccess_try_nospec covers get_user_try.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727416953.33451.10508284228526170604.stgit@dwillia2-desk3.amr.corp.intel.com
64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_UACCESS_32_H
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#define _ASM_X86_UACCESS_32_H
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/*
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* User space memory access functions
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*/
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#include <linux/string.h>
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#include <asm/asm.h>
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#include <asm/page.h>
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unsigned long __must_check __copy_user_ll
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(void *to, const void *from, unsigned long n);
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unsigned long __must_check __copy_from_user_ll_nocache_nozero
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(void *to, const void __user *from, unsigned long n);
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static __always_inline unsigned long __must_check
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raw_copy_to_user(void __user *to, const void *from, unsigned long n)
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{
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return __copy_user_ll((__force void *)to, from, n);
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}
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static __always_inline unsigned long
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raw_copy_from_user(void *to, const void __user *from, unsigned long n)
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{
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if (__builtin_constant_p(n)) {
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unsigned long ret;
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switch (n) {
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case 1:
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ret = 0;
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__uaccess_begin_nospec();
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__get_user_asm_nozero(*(u8 *)to, from, ret,
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"b", "b", "=q", 1);
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__uaccess_end();
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return ret;
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case 2:
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ret = 0;
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__uaccess_begin_nospec();
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__get_user_asm_nozero(*(u16 *)to, from, ret,
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"w", "w", "=r", 2);
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__uaccess_end();
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return ret;
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case 4:
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ret = 0;
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__uaccess_begin_nospec();
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__get_user_asm_nozero(*(u32 *)to, from, ret,
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"l", "k", "=r", 4);
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__uaccess_end();
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return ret;
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}
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}
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return __copy_user_ll(to, (__force const void *)from, n);
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}
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static __always_inline unsigned long
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__copy_from_user_inatomic_nocache(void *to, const void __user *from,
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unsigned long n)
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{
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return __copy_from_user_ll_nocache_nozero(to, from, n);
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}
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#endif /* _ASM_X86_UACCESS_32_H */
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