[tip: ras/core] x86/mce: Check regs before accessing it

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the ras/core branch of tip:

Commit-ID:     1acd85feba81084fcef00b73fc1601e42b77c5d8
Gitweb:        https://git.kernel.org/tip/1acd85feba81084fcef00b73fc1601e42b77c5d8
Author:        Borislav Petkov <bp@xxxxxxx>
AuthorDate:    Fri, 17 Dec 2021 16:49:25 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Mon, 20 Dec 2021 11:41:02 +01:00

x86/mce: Check regs before accessing it

Commit in Fixes accesses pt_regs before checking whether it is NULL or
not. Make sure the NULL pointer check happens first.

Fixes: 0a5b288e85bb ("x86/mce: Prevent severity computation from being instrumented")
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Link: https://lore.kernel.org/r/20211217102029.GA29708@kili
---
 arch/x86/kernel/cpu/mce/severity.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index a326467..7aa2bda 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -222,6 +222,9 @@ static bool is_copy_from_user(struct pt_regs *regs)
 	struct insn insn;
 	int ret;
 
+	if (!regs)
+		return false;
+
 	if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip, MAX_INSN_SIZE))
 		return false;
 
@@ -283,7 +286,7 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
 	switch (fixup_type) {
 	case EX_TYPE_UACCESS:
 	case EX_TYPE_COPY:
-		if (!regs || !copy_user)
+		if (!copy_user)
 			return IN_KERNEL;
 		m->kflags |= MCE_IN_KERNEL_COPYIN;
 		fallthrough;