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https://github.com/torvalds/linux
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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>
101 lines
2.4 KiB
C
101 lines
2.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/bitops.h>
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#include <linux/fault-inject-usercopy.h>
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#include <linux/instrumented.h>
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#include <linux/uaccess.h>
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#include <linux/nospec.h>
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/* out-of-line parts */
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#ifndef INLINE_COPY_FROM_USER
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unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
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{
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unsigned long res = n;
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might_fault();
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if (!should_fail_usercopy() && likely(access_ok(from, n))) {
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/*
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* Ensure that bad access_ok() speculation will not
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* lead to nasty side effects *after* the copy is
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* finished:
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*/
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barrier_nospec();
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instrument_copy_from_user_before(to, from, n);
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res = raw_copy_from_user(to, from, n);
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instrument_copy_from_user_after(to, from, n, res);
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}
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if (unlikely(res))
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memset(to + (n - res), 0, res);
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return res;
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}
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EXPORT_SYMBOL(_copy_from_user);
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#endif
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#ifndef INLINE_COPY_TO_USER
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unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
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{
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might_fault();
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if (should_fail_usercopy())
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return n;
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if (likely(access_ok(to, n))) {
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instrument_copy_to_user(to, from, n);
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n = raw_copy_to_user(to, from, n);
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}
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return n;
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}
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EXPORT_SYMBOL(_copy_to_user);
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#endif
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/**
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* check_zeroed_user: check if a userspace buffer only contains zero bytes
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* @from: Source address, in userspace.
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* @size: Size of buffer.
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*
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* This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
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* userspace addresses (and is more efficient because we don't care where the
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* first non-zero byte is).
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*
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* Returns:
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* * 0: There were non-zero bytes present in the buffer.
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* * 1: The buffer was full of zero bytes.
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* * -EFAULT: access to userspace failed.
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*/
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int check_zeroed_user(const void __user *from, size_t size)
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{
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unsigned long val;
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uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
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if (unlikely(size == 0))
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return 1;
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from -= align;
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size += align;
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if (!user_read_access_begin(from, size))
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return -EFAULT;
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unsafe_get_user(val, (unsigned long __user *) from, err_fault);
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if (align)
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val &= ~aligned_byte_mask(align);
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while (size > sizeof(unsigned long)) {
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if (unlikely(val))
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goto done;
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from += sizeof(unsigned long);
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size -= sizeof(unsigned long);
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unsafe_get_user(val, (unsigned long __user *) from, err_fault);
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}
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if (size < sizeof(unsigned long))
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val &= aligned_byte_mask(size);
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done:
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user_read_access_end();
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return (val == 0);
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err_fault:
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user_read_access_end();
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return -EFAULT;
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}
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EXPORT_SYMBOL(check_zeroed_user);
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