x86/fpu: Use validate_xstate_header() to validate the xstate_header in __fpu__restore...

Tighten the checks in __fpu__restore_sig() and update comments.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kevin Hao <haokexin@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Halcrow <mhalcrow@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: kernel-hardening@lists.openwall.com
Link: http://lkml.kernel.org/r/20170924105913.9157-4-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 7fa3bdb331e91b84dae0035c8dbb7878e684dddc..fb639e70048f58dfaef5576ab73e6998fa8ebbd1 100644 (file)
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -214,8 +214,11 @@ sanitize_restored_xstate(struct task_struct *tsk,
        struct xstate_header *header = &xsave->header;
 
        if (use_xsave()) {
-               /* These bits must be zero. */
-               memset(header->reserved, 0, 48);
+               /*
+                * Note: we don't need to zero the reserved bits in the
+                * xstate_header here because we either didn't copy them at all,
+                * or we checked earlier that they aren't set.
+                */
 
                /*
                 * Init the state that is not present in the memory
@@ -224,7 +227,7 @@ sanitize_restored_xstate(struct task_struct *tsk,
                if (fx_only)
                        header->xfeatures = XFEATURE_MASK_FPSSE;
                else
-                       header->xfeatures &= (xfeatures_mask & xfeatures);
+                       header->xfeatures &= xfeatures;
        }
 
        if (use_fxsr()) {
@@ -308,7 +311,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
                /*
                 * For 32-bit frames with fxstate, copy the user state to the
                 * thread's fpu state, reconstruct fxstate from the fsave
-                * header. Sanitize the copied state etc.
+                * header. Validate and sanitize the copied state.
                 */
                struct fpu *fpu = &tsk->thread.fpu;
                struct user_i387_ia32_struct env;
@@ -329,9 +332,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
                } else {
                        err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
 
-                       /* xcomp_bv must be 0 when using uncompacted format */
-                       if (!err && state_size > offsetof(struct xregs_state, header) && fpu->state.xsave.header.xcomp_bv)
-                               err = -EINVAL;
+                       if (!err && state_size > offsetof(struct xregs_state, header))
+                               err = validate_xstate_header(&fpu->state.xsave.header);
                }
 
                if (err || __copy_from_user(&env, buf, sizeof(env))) {