The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 484cea4f362e1eeb5c869abbfb5f90eae6421b38 Gitweb: https://git.kernel.org/tip/484cea4f362e1eeb5c869abbfb5f90eae6421b38 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Tue, 08 Jun 2021 16:36:18 +02:00 Committer: Borislav Petkov bp@suse.de CommitterDate: Wed, 09 Jun 2021 09:28:21 +02:00

x86/fpu: Prevent state corruption in __fpu__restore_sig()

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@syzkaller.appspotmail.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Borislav Petkov bp@suse.de Acked-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Rik van Riel riel@surriel.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210608144345.611833074@linutronix.de --- arch/x86/kernel/fpu/signal.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index a4ec653..d5bc96a 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -405,14 +405,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) 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;