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| author | Dave Hansen <dave.hansen@linux.intel.com> | 2023-02-21 12:30:15 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-02-25 11:50:31 +0100 |
| commit | e0fbff18bbcee4f07d46bee172803fad63f6f4dd (patch) | |
| tree | af675c303bb80d67006dbbb0ad75afeef032a548 /include/linux | |
| parent | d21f4dae47b4f79c6932af4aef98de9e7dea9930 (diff) | |
| download | linux-stable-e0fbff18bbcee4f07d46bee172803fad63f6f4dd.tar.gz linux-stable-e0fbff18bbcee4f07d46bee172803fad63f6f4dd.tar.bz2 linux-stable-e0fbff18bbcee4f07d46bee172803fad63f6f4dd.zip | |
uaccess: Add speculation barrier to copy_from_user()
commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/nospec.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/nospec.h b/include/linux/nospec.h index 0c5ef54fd416..207ef2a20e48 100644 --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -9,6 +9,10 @@ struct task_struct; +#ifndef barrier_nospec +# define barrier_nospec() do { } while (0) +#endif + /** * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise * @index: array element index |