This is a note to let you know that I've just added the patch titled
x86/fpu: Prevent state corruption in __fpu__restore_sig()
to the 5.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-fpu-prevent-state-corruption-in-__fpu__restore_sig.patch
and it can be found in the queue-5.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 484cea4f362e1eeb5c869abbfb5f90eae6421b38 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Tue, 8 Jun 2021 16:36:18 +0200
Subject: x86/fpu: Prevent state corruption in __fpu__restore_sig()
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 484cea4f362e1eeb5c869abbfb5f90eae6421b38 upstream.
The non-compacted slowpath uses __copy_from_user() and copies the entire
user buffer into the kernel buffer, verbatim. This means that the kernel
buffer may now contain entirely invalid state on which XRSTOR will #GP.
validate_user_xstate_header() can detect some of that corruption, but that
leaves the onus on callers to clear the buffer.
Prior to XSAVES support, it was possible just to reinitialize the buffer,
completely, but with supervisor states that is not longer possible as the
buffer clearing code split got it backwards. Fixing that is possible but
not corrupting the state in the first place is more robust.
Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate()
which validates the XSAVE header contents before copying the actual states
to the kernel. copy_user_to_xstate() was previously only called for
compacted-format kernel buffers, but it works for both compacted and
non-compacted forms.
Using it for the non-compacted form is slower because of multiple
__copy_from_user() operations, but that cost is less important than robust
code in an already slow path.
[ Changelog polished by Dave Hansen ]
Fixes: b860eb8dce59 ("x86/fpu/xstate: Define new functions for clearing fpregs and xstates")
Reported-by: syzbot+2067e764dbcd10721e2e@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20210608144345.611833074@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/fpu/signal.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -405,14 +405,7 @@ static int __fpu__restore_sig(void __use
if (use_xsave() && !fx_only) {
u64 init_bv = xfeatures_mask_user() & ~user_xfeatures;
- if (using_compacted_format()) {
- ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
- } else {
- ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
-
- if (!ret && state_size > offsetof(struct xregs_state, header))
- ret = validate_user_xstate_header(&fpu->state.xsave.header);
- }
+ ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
if (ret)
goto err_out;
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-5.12/x86-process-check-pf_kthread-and-not-current-mm-for-kernel-threads.patch
queue-5.12/x86-pkru-write-hardware-init-value-to-pkru-when-xstate-is-init.patch
queue-5.12/x86-fpu-prevent-state-corruption-in-__fpu__restore_sig.patch
queue-5.12/crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch
queue-5.12/x86-fpu-invalidate-fpu-state-after-a-failed-xrstor-from-a-user-buffer.patch
queue-5.12/x86-fpu-reset-state-for-all-signal-restore-failures.patch
