Re: [PATCH 14/23] tracing/kprobes: handle mixed kernel/userspace probes better

Masami Hiramatsu
2020-05-22T00:04:59Z

On Thu, 21 May 2020 17:22:52 +0200
Christoph Hellwig <hch@lst.de> wrote:

> Instead of using the dangerous probe_kernel_read and strncpy_from_unsafe
> helpers, rework probes to try a user probe based on the address if the
> architecture has a common address space for kernel and userspace.
>

This looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you!

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> kernel/trace/trace_kprobe.c | 72 ++++++++++++++++++++++---------------
> 1 file changed, 43 insertions(+), 29 deletions(-)
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 4325f9e7fadaa..4aeaef53ba970 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1200,6 +1200,15 @@ static const struct file_operations kprobe_profile_ops = {
>
> /* Kprobe specific fetch functions */
>
> +/* Return the length of string -- including null terminal byte */
> +static nokprobe_inline int
> +fetch_store_strlen_user(unsigned long addr)
> +{
> + const void __user *uaddr = (__force const void __user *)addr;
> +
> + return strnlen_user_nofault(uaddr, MAX_STRING_SIZE);
> +}
> +
> /* Return the length of string -- including null terminal byte */
> static nokprobe_inline int
> fetch_store_strlen(unsigned long addr)
> @@ -1207,30 +1216,27 @@ fetch_store_strlen(unsigned long addr)
> int ret, len = 0;
> u8 c;
>
> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> + if (addr < TASK_SIZE)
> + return fetch_store_strlen_user(addr);
> +#endif
> +
> do {
> - ret = probe_kernel_read(&c, (u8 *)addr + len, 1);
> + ret = probe_kernel_read_strict(&c, (u8 *)addr + len, 1);
> len++;
> } while (c && ret == 0 && len < MAX_STRING_SIZE);
>
> return (ret < 0) ? ret : len;
> }
>
> -/* Return the length of string -- including null terminal byte */
> -static nokprobe_inline int
> -fetch_store_strlen_user(unsigned long addr)
> -{
> - const void __user *uaddr = (__force const void __user *)addr;
> -
> - return strnlen_user_nofault(uaddr, MAX_STRING_SIZE);
> -}
> -
> /*
> - * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
> - * length and relative data location.
> + * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
> + * with max length and relative data location.
> */
> static nokprobe_inline int
> -fetch_store_string(unsigned long addr, void *dest, void *base)
> +fetch_store_string_user(unsigned long addr, void *dest, void *base)
> {
> + const void __user *uaddr = (__force const void __user *)addr;
> int maxlen = get_loc_len(*(u32 *)dest);
> void *__dest;
> long ret;
> @@ -1240,11 +1246,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
>
> __dest = get_loc_data(dest, base);
>
> - /*
> - * Try to get string again, since the string can be changed while
> - * probing.
> - */
> - ret = strncpy_from_unsafe(__dest, (void *)addr, maxlen);
> + ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
> if (ret >= 0)
> *(u32 *)dest = make_data_loc(ret, __dest - base);
>
> @@ -1252,35 +1254,37 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
> }
>
> /*
> - * Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
> - * with max length and relative data location.
> + * Fetch a null-terminated string. Caller MUST set *(u32 *)buf with max
> + * length and relative data location.
> */
> static nokprobe_inline int
> -fetch_store_string_user(unsigned long addr, void *dest, void *base)
> +fetch_store_string(unsigned long addr, void *dest, void *base)
> {
> - const void __user *uaddr = (__force const void __user *)addr;
> int maxlen = get_loc_len(*(u32 *)dest);
> void *__dest;
> long ret;
>
> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> + if ((unsigned long)addr < TASK_SIZE)
> + return fetch_store_string_user(addr, dest, base);
> +#endif
> +
> if (unlikely(!maxlen))
> return -ENOMEM;
>
> __dest = get_loc_data(dest, base);
>
> - ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
> + /*
> + * Try to get string again, since the string can be changed while
> + * probing.
> + */
> + ret = strncpy_from_user_nofault(__dest, (void *)addr, maxlen);
> if (ret >= 0)
> *(u32 *)dest = make_data_loc(ret, __dest - base);
>
> return ret;
> }
>
> -static nokprobe_inline int
> -probe_mem_read(void *dest, void *src, size_t size)
> -{
> - return probe_kernel_read(dest, src, size);
> -}
> -
> static nokprobe_inline int
> probe_mem_read_user(void *dest, void *src, size_t size)
> {
> @@ -1289,6 +1293,16 @@ probe_mem_read_user(void *dest, void *src, size_t size)
> return probe_user_read(dest, uaddr, size);
> }
>
> +static nokprobe_inline int
> +probe_mem_read(void *dest, void *src, size_t size)
> +{
> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> + if ((unsigned long)src < TASK_SIZE)
> + return probe_mem_read_user(dest, src, size);
> +#endif
> + return probe_kernel_read_strict(dest, src, size);
> +}
> +
> /* Note that we don't verify it, since the code does not come from user space */
> static int
> process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
> --
> 2.26.2
>

--
Masami Hiramatsu <mhiramat@kernel.org>