[tip: x86/fpu] x86/fpu/signal: Move xstate clearing out of copy_fpregs_to_sigframe()

[tip-bot2 for Thomas Gleixner]

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

Commit-ID:     fcfb7163329ce832aafef31f26345ef5e8642a17
Gitweb:        https://git.kernel.org/tip/fcfb7163329ce832aafef31f26345ef5e8642a17
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Wed, 08 Sep 2021 15:29:30 +02:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 14 Sep 2021 21:10:03 +02:00

x86/fpu/signal: Move xstate clearing out of copy_fpregs_to_sigframe()

When the direct saving of the FPU registers to the user space sigframe
fails, copy_fpregs_to_sigframe() attempts to clear the user buffer.

The most likely reason for such a fail is a page fault. As
copy_fpregs_to_sigframe() is invoked with pagefaults disabled the chance
that __clear_user() succeeds is minuscule.

Move the clearing out into the caller which replaces the
fault_in_pages_writeable() in that error handling path.

The return value confusion will be cleaned up separately.

Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210908132525.679356300@xxxxxxxxxxxxx
---
 arch/x86/kernel/fpu/signal.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 5ca3ce9..c4abbd9 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -136,18 +136,12 @@ static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
 
 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
 {
-	int err;
-
 	if (use_xsave())
-		err = xsave_to_user_sigframe(buf);
-	else if (use_fxsr())
-		err = fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
+		return xsave_to_user_sigframe(buf);
+	if (use_fxsr())
+		return fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
 	else
-		err = fnsave_to_user_sigframe((struct fregs_state __user *) buf);
-
-	if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
-		err = -EFAULT;
-	return err;
+		return fnsave_to_user_sigframe((struct fregs_state __user *) buf);
 }
 
 /*
@@ -218,9 +212,9 @@ retry:
 	fpregs_unlock();
 
 	if (ret) {
-		if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
+		if (!__clear_user(buf_fx, fpu_user_xstate_size))
 			goto retry;
-		return -EFAULT;
+		return -1;
 	}
 
 	/* Save the fsave header for the 32-bit frames. */