Hi Christoph,
On Wed, 13 May 2020 18:00:34 +0200
Christoph Hellwig <hch@xxxxxx> wrote:
> Provide alternative versions of probe_kernel_read, probe_kernel_write
> and strncpy_from_kernel_unsafe that don't need set_fs magic, but instead
> use arch hooks that are modelled after unsafe_{get,put}_user to access
> kernel memory in an exception safe way.
This patch seems to introduce new implementation of probe_kernel_read/write()
and strncpy_from_kernel_unsafe(), but also drops copy_from/to_kernel_nofault()
and strncpy_from_kernel_nofault() if HAVE_ARCH_PROBE_KERNEL is defined.
In the result, this cause a link error with BPF and kprobe events.
BTW, what is the difference of *_unsafe() and *_nofault()?
(maybe we make those to *_nofault() finally?)
Thank you,
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> mm/maccess.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 76 insertions(+)
>
> diff --git a/mm/maccess.c b/mm/maccess.c
> index 9773e2253b495..e9efe2f98e34a 100644
> --- a/mm/maccess.c
> +++ b/mm/maccess.c
> @@ -12,6 +12,81 @@ bool __weak probe_kernel_read_allowed(void *dst, const void *unsafe_src,
> return true;
> }
>
> +#ifdef HAVE_ARCH_PROBE_KERNEL
> +
> +#define probe_kernel_read_loop(dst, src, len, type, err_label) \
> + while (len >= sizeof(type)) { \
> + arch_kernel_read(dst, src, type, err_label); \
> + dst += sizeof(type); \
> + src += sizeof(type); \
> + len -= sizeof(type); \
> + }
> +
> +long probe_kernel_read(void *dst, const void *src, size_t size)
> +{
> + if (!probe_kernel_read_allowed(dst, src, size))
> + return -EFAULT;
> +
> + pagefault_disable();
> + probe_kernel_read_loop(dst, src, size, u64, Efault);
> + probe_kernel_read_loop(dst, src, size, u32, Efault);
> + probe_kernel_read_loop(dst, src, size, u16, Efault);
> + probe_kernel_read_loop(dst, src, size, u8, Efault);
> + pagefault_enable();
> + return 0;
> +Efault:
> + pagefault_enable();
> + return -EFAULT;
> +}
> +EXPORT_SYMBOL_GPL(probe_kernel_read);
> +
> +#define probe_kernel_write_loop(dst, src, len, type, err_label) \
> + while (len >= sizeof(type)) { \
> + arch_kernel_write(dst, src, type, err_label); \
> + dst += sizeof(type); \
> + src += sizeof(type); \
> + len -= sizeof(type); \
> + }
> +
> +long probe_kernel_write(void *dst, const void *src, size_t size)
> +{
> + pagefault_disable();
> + probe_kernel_write_loop(dst, src, size, u64, Efault);
> + probe_kernel_write_loop(dst, src, size, u32, Efault);
> + probe_kernel_write_loop(dst, src, size, u16, Efault);
> + probe_kernel_write_loop(dst, src, size, u8, Efault);
> + pagefault_enable();
> + return 0;
> +Efault:
> + pagefault_enable();
> + return -EFAULT;
> +}
> +
> +long strncpy_from_kernel_unsafe(char *dst, const void *unsafe_addr, long count)
> +{
> + const void *src = unsafe_addr;
> +
> + if (unlikely(count <= 0))
> + return 0;
> + if (!probe_kernel_read_allowed(dst, unsafe_addr, count))
> + return -EFAULT;
> +
> + pagefault_disable();
> + do {
> + arch_kernel_read(dst, src, u8, Efault);
> + dst++;
> + src++;
> + } while (dst[-1] && src - unsafe_addr < count);
> + pagefault_enable();
> +
> + dst[-1] = '\0';
> + return src - unsafe_addr;
> +Efault:
> + pagefault_enable();
> + dst[-1] = '\0';
> + return -EFAULT;
> +}
> +#else /* HAVE_ARCH_PROBE_KERNEL */
> /**
> * probe_kernel_read(): safely attempt to read from kernel-space
> * @dst: pointer to the buffer that shall take the data
> @@ -114,6 +189,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
>
> return ret ? -EFAULT : src - unsafe_addr;
> }
> +#endif /* HAVE_ARCH_PROBE_KERNEL */
>
> /**
> * probe_user_read(): safely attempt to read from a user-space location
> --
> 2.26.2
>
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
