On Tue, 19 May 2020 15:44:42 +0200
Christoph Hellwig <hch@xxxxxx> wrote:
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 2f6737cc53e6c..82da20e712507 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1208,7 +1208,13 @@ fetch_store_strlen(unsigned long addr)
> u8 c;
>
> do {
> - ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
> + if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) &&
> + (unsigned long)addr < TASK_SIZE) {
> + ret = probe_user_read(&c,
> + (__force u8 __user *)addr + len, 1);
> + } else {
> + ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
> + }
> len++;
> } while (c && ret == 0 && len < MAX_STRING_SIZE);
To avoid redundant check in the loop, we can use strnlen_user_nofault() out of
the loop. Something like below.
...
u8 c;
if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) &&
(unsigned long)addr < TASK_SIZE) {
return strnlen_user_nofault((__force u8 __user *)addr, MAX_STRING_SIZE);
do {
ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
len++;
} while (c && ret == 0 && len < MAX_STRING_SIZE);
...
This must work because we must not have a string that continues across
kernel space and user space.
Thank you,
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
