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@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20211217102029.GA29708@kili

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index a326467..7aa2bda 100644 (file)
--- 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;