From: Thomas Gleixner tglx@linutronix.de
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 Cc: stable@vger.kernel.org --- V2: Removed the make validate_user_xstate_header() static hunks (Borislav) --- 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;