[tip: x86/fpu] x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

[tip-bot2 for Andy Lutomirski]

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

Commit-ID:     145e9e0d8c6fada4a40f9fc65b34658077874d9c
Gitweb:        https://git.kernel.org/tip/145e9e0d8c6fada4a40f9fc65b34658077874d9c
Author:        Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate:    Wed, 23 Jun 2021 14:01:40 +02:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 23 Jun 2021 17:49:46 +02:00

x86/fpu: Fail ptrace() requests that try to set invalid MXCSR values

There is no benefit from accepting and silently changing an invalid MXCSR
value supplied via ptrace().  Instead, return -EINVAL on invalid input.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210623121452.613614842@xxxxxxxxxxxxx
---
 arch/x86/kernel/fpu/regset.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index f24ce87..5610f77 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -63,8 +63,9 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 	if (ret)
 		return ret;
 
-	/* Mask invalid MXCSR bits (for historical reasons). */
-	newstate.mxcsr &= mxcsr_feature_mask;
+	/* Do not allow an invalid MXCSR value. */
+	if (newstate.mxcsr & ~mxcsr_feature_mask)
+		return -EINVAL;
 
 	fpu__prepare_write(fpu);