x86/fpu: Limit xstate copy size in xstateregs_set()

BugLink: https://bugs.launchpad.net/bugs/1939440
[ Upstream commit 07d6688b22e09be465652cf2da0da6bf86154df6 ]

If the count argument is larger than the xstate size, this will happily
copy beyond the end of xstate.

Fixes: 91c3dba7dbc1 ("x86/fpu/xstate: Fix PTRACE frames for XSAVES")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121452.120741557@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index d652b939ccfb5865f8a8383e04e71adfe450c1e1..68e1fb66e701bd81ac316bce15305ca6c147530d 100644 (file)
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -124,7 +124,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
        /*
         * A whole standard-format XSAVE buffer is needed:
         */
-       if ((pos != 0) || (count < fpu_user_xstate_size))
+       if (pos != 0 || count != fpu_user_xstate_size)
                return -EFAULT;
 
        xsave = &fpu->state.xsave;