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SubjectRe: [PATCH] arm64: ftrace: don't dereference a probably invalid address
Date
> On Mon, 7 Jun 2021 22:15:22 +0800
> Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:
>
> > And the crash is becuase kernel trying to read *rec->ip in print_ip_ins() if
> > ftrace_bug() get error code -EINVAL.
>
> Right, so the actual fix should be something like this:
>
> [ not tested, nor even compiled ]
>
> -- Steve
>

I just test this patch, and turns out it work well.
All my modification is only rename copy_from_kernel_nofault
into probe_kernel_read because the older kernel version
I use.
Then the kernel will show the error mesage instead of panic as following.

[ 0.000000] ftrace failed to modify
[ 0.000000] [<0000000000000020>] 0x20
[ 0.000000] actual: [FAULT](0000000000000020)

Should I resend this patch as v2?
Or you will upstream this fix?

>
> 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)", 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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