From dc8aa31a7ac2c4290ea974c13cb0094e08f8948f Mon Sep 17 00:00:00 2001 From: "Chang S. Bae" Date: Tue, 10 Dec 2024 17:45:00 -0800 Subject: [PATCH] x86/fpu: Refine and simplify the magic number check during signal return Before restoring xstate from the user space buffer, the kernel performs sanity checks on these magic numbers: magic1 in the software reserved area, and magic2 at the end of XSAVE region. The position of magic2 is calculated based on the xstate size derived from the user space buffer. But, the in-kernel record is directly available and reliable for this purpose. This reliance on user space data is also inconsistent with the recent fix in: d877550eaf2d ("x86/fpu: Stop relying on userspace for info to fault in xsave buffer") Simply use fpstate->user_size, and then get rid of unnecessary size-evaluation code. Signed-off-by: Chang S. Bae Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Dave Hansen Link: https://lore.kernel.org/r/20241211014500.3738-1-chang.seok.bae@intel.com --- arch/x86/kernel/fpu/signal.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 8f62e0666dea5..6c69cb28b2983 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -27,19 +27,14 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf, struct _fpx_sw_bytes *fx_sw) { - int min_xstate_size = sizeof(struct fxregs_state) + - sizeof(struct xstate_header); void __user *fpstate = fxbuf; unsigned int magic2; if (__copy_from_user(fx_sw, &fxbuf->sw_reserved[0], sizeof(*fx_sw))) return false; - /* Check for the first magic field and other error scenarios. */ - if (fx_sw->magic1 != FP_XSTATE_MAGIC1 || - fx_sw->xstate_size < min_xstate_size || - fx_sw->xstate_size > current->thread.fpu.fpstate->user_size || - fx_sw->xstate_size > fx_sw->extended_size) + /* Check for the first magic field */ + if (fx_sw->magic1 != FP_XSTATE_MAGIC1) goto setfx; /* @@ -48,7 +43,7 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf, * fpstate layout with out copying the extended state information * in the memory layout. */ - if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))) + if (__get_user(magic2, (__u32 __user *)(fpstate + current->thread.fpu.fpstate->user_size))) return false; if (likely(magic2 == FP_XSTATE_MAGIC2))