ftrace: Do not blindly read the ip address in ftrace_bug()

It was reported that a bug on arm64 caused a bad ip address to be used for
updating into a nop in ftrace_init(), but the error path (rightfully)
returned -EINVAL and not -EFAULT, as the bug caused more than one error to
occur. But because -EINVAL was returned, the ftrace_bug() tried to report
what was at the location of the ip address, and read it directly. This
caused the machine to panic, as the ip was not pointing to a valid memory
address.

Instead, read the ip address with copy_from_kernel_nofault() to safely
access the memory, and if it faults, report that the address faulted,
otherwise report what was in that location.

Link: https://lore.kernel.org/lkml/20210607032329.28671-1-mark-pk.tsai@mediatek.com/

Cc: stable@vger.kernel.org
Fixes: 05736a42 ("ftrace: warn on failure to disable mcount callers")
Reported-by: default avatarMark-PK Tsai <mark-pk.tsai@mediatek.com>
Tested-by: default avatarMark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 824afd55
......@@ -1967,12 +1967,18 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
static void print_ip_ins(const char *fmt, const unsigned char *p)
{
char ins[MCOUNT_INSN_SIZE];
int i;
if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
printk(KERN_CONT "%s[FAULT] %px\n", fmt, p);
return;
}
printk(KERN_CONT "%s", fmt);
for (i = 0; i < MCOUNT_INSN_SIZE; i++)
printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);
}
enum ftrace_bug_type ftrace_bug_type;
......
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