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74e19ef0ff
The results of "access_ok()" can be mis-speculated. The result is that you can end speculatively: if (access_ok(from, size)) // Right here even for bad from/size combinations. On first glance, it would be ideal to just add a speculation barrier to "access_ok()" so that its results can never be mis-speculated. But there are lots of system calls just doing access_ok() via "copy_to_user()" and friends (example: fstat() and friends). Those are generally not problematic because they do not _consume_ data from userspace other than the pointer. They are also very quick and common system calls that should not be needlessly slowed down. "copy_from_user()" on the other hand uses a user-controller pointer and is frequently followed up with code that might affect caches. Take something like this: if (!copy_from_user(&kernelvar, uptr, size)) do_something_with(kernelvar); If userspace passes in an evil 'uptr' that *actually* points to a kernel addresses, and then do_something_with() has cache (or other) side-effects, it could allow userspace to infer kernel data values. Add a barrier to the common copy_from_user() code to prevent mis-speculated values which happen after the copy. Also add a stub for architectures that do not define barrier_nospec(). This makes the macro usable in generic code. Since the barrier is now usable in generic code, the x86 #ifdef in the BPF code can also go away. Reported-by: Jordy Zomer <jordyzomer@google.com> Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Daniel Borkmann <daniel@iogearbox.net> # BPF bits Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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// Copyright(c) 2018 Linus Torvalds. All rights reserved.
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// Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
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// Copyright(c) 2018 Intel Corporation. All rights reserved.
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#ifndef _LINUX_NOSPEC_H
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#define _LINUX_NOSPEC_H
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#include <linux/compiler.h>
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#include <asm/barrier.h>
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struct task_struct;
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#ifndef barrier_nospec
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# define barrier_nospec() do { } while (0)
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#endif
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/**
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* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
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* @index: array element index
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* @size: number of elements in array
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*
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* When @index is out of bounds (@index >= @size), the sign bit will be
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* set. Extend the sign bit to all bits and invert, giving a result of
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* zero for an out of bounds index, or ~0 if within bounds [0, @size).
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*/
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#ifndef array_index_mask_nospec
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static inline unsigned long array_index_mask_nospec(unsigned long index,
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unsigned long size)
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{
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/*
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* Always calculate and emit the mask even if the compiler
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* thinks the mask is not needed. The compiler does not take
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* into account the value of @index under speculation.
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*/
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OPTIMIZER_HIDE_VAR(index);
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return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
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}
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#endif
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/*
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* array_index_nospec - sanitize an array index after a bounds check
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*
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* For a code sequence like:
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*
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* if (index < size) {
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* index = array_index_nospec(index, size);
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* val = array[index];
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* }
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*
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* ...if the CPU speculates past the bounds check then
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* array_index_nospec() will clamp the index within the range of [0,
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* size).
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*/
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#define array_index_nospec(index, size) \
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({ \
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typeof(index) _i = (index); \
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typeof(size) _s = (size); \
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unsigned long _mask = array_index_mask_nospec(_i, _s); \
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\
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BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
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BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
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\
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(typeof(_i)) (_i & _mask); \
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})
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/* Speculation control prctl */
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int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
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int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
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unsigned long ctrl);
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/* Speculation control for seccomp enforced mitigation */
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void arch_seccomp_spec_mitigate(struct task_struct *task);
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#endif /* _LINUX_NOSPEC_H */
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