From: "Steven Rostedt (VMware)" rostedt@goodmis.org

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.co...

Cc: stable@vger.kernel.org Fixes: 05736a427f7e1 ("ftrace: warn on failure to disable mcount callers") Reported-by: Mark-PK Tsai mark-pk.tsai@mediatek.com Tested-by: Mark-PK Tsai mark-pk.tsai@mediatek.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/ftrace.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 2e8a3fde7104..72ef4dccbcc4 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -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;