On 31.07.23 23:50, 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> 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. */
Having a comment at this indentation level looks for the else case looks kind of weird.
(does that comment still apply?) -- Cheers, David / dhildenb
