On Mon, Jul 31, 2023 at 10:50:21PM +0100, Lorenzo Stoakes wrote:
> Some architectures do not populate the entire range categorised by
> KCORE_TEXT, so we must ensure that the kernel address we read from is
> valid.
>
> Unfortunately there is no solution currently available to do so with a
> purely iterator solution so reinstate the bounce buffer in this instance so
> we can use copy_from_kernel_nofault() in order to avoid page faults when
> regions are unmapped.
>
> This change partly reverts commit 2e1c0170771e ("fs/proc/kcore: avoid
> bounce buffer for ktext data"), reinstating the bounce buffer, but adapts
> the code to continue to use an iterator.
>
> Fixes: 2e1c0170771e ("fs/proc/kcore: avoid bounce buffer for ktext data")
> Reported-by: Jiri Olsa <olsajiri@xxxxxxxxx>
it fixed my issue, thanks
Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
jirka
> Closes: https://lore.kernel.org/all/ZHc2fm+9daF6cgCE@krava
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> ---
> fs/proc/kcore.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 9cb32e1a78a0..3bc689038232 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -309,6 +309,8 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
>
> static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> {
> + struct file *file = iocb->ki_filp;
> + char *buf = file->private_data;
> loff_t *fpos = &iocb->ki_pos;
> size_t phdrs_offset, notes_offset, data_offset;
> size_t page_offline_frozen = 1;
> @@ -554,11 +556,22 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> fallthrough;
> case KCORE_VMEMMAP:
> case KCORE_TEXT:
> + /*
> + * Sadly we must use a bounce buffer here to be able to
> + * make use of copy_from_kernel_nofault(), as these
> + * memory regions might not always be mapped on all
> + * architectures.
> + */
> + if (copy_from_kernel_nofault(buf, (void *)start, tsz)) {
> + if (iov_iter_zero(tsz, iter) != tsz) {
> + ret = -EFAULT;
> + goto out;
> + }
> /*
> * We use _copy_to_iter() to bypass usermode hardening
> * which would otherwise prevent this operation.
> */
> - if (_copy_to_iter((char *)start, tsz, iter) != tsz) {
> + } else if (_copy_to_iter(buf, tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> @@ -595,6 +608,10 @@ static int open_kcore(struct inode *inode, struct file *filp)
> if (ret)
> return ret;
>
> + filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + if (!filp->private_data)
> + return -ENOMEM;
> +
> if (kcore_need_update)
> kcore_update_ram();
> if (i_size_read(inode) != proc_root_kcore->size) {
> @@ -605,9 +622,16 @@ static int open_kcore(struct inode *inode, struct file *filp)
> return 0;
> }
>
> +static int release_kcore(struct inode *inode, struct file *file)
> +{
> + kfree(file->private_data);
> + return 0;
> +}
> +
> static const struct proc_ops kcore_proc_ops = {
> .proc_read_iter = read_kcore_iter,
> .proc_open = open_kcore,
> + .proc_release = release_kcore,
> .proc_lseek = default_llseek,
> };
>
> --
> 2.41.0
>
