On Thu, Mar 23, 2023 at 10:15:16AM +0000, Lorenzo Stoakes wrote:
> Commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
> introduced the use of a bounce buffer to retrieve kernel text data for
> /proc/kcore in order to avoid failures arising from hardened user copies
> enabled by CONFIG_HARDENED_USERCOPY in check_kernel_text_object().
>
> We can avoid doing this if instead of copy_to_user() we use _copy_to_user()
> which bypasses the hardening check. This is more efficient than using a
> bounce buffer and simplifies the code.
>
> We do so as part an overall effort to eliminate bounce buffer usage in the
> function with an eye to converting it an iterator read.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
hi,
sorry for late feedback, but looks like this one breaks reading
/proc/kcore with objdump for me:
# cat /proc/kallsyms | grep ksys_read
ffffffff8150ebc0 T ksys_read
# objdump -d --start-address=0xffffffff8150ebc0 --stop-address=0xffffffff8150ebd0 /proc/kcore
/proc/kcore: file format elf64-x86-64
objdump: Reading section load1 failed because: Bad address
reverting this makes it work again
thanks,
jirka
> ---
> fs/proc/kcore.c | 17 +++++------------
> 1 file changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 71157ee35c1a..556f310d6aa4 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -541,19 +541,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> case KCORE_VMEMMAP:
> case KCORE_TEXT:
> /*
> - * Using bounce buffer to bypass the
> - * hardened user copy kernel text checks.
> + * We use _copy_to_user() to bypass usermode hardening
> + * which would otherwise prevent this operation.
> */
> - if (copy_from_kernel_nofault(buf, (void *)start, tsz)) {
> - if (clear_user(buffer, tsz)) {
> - ret = -EFAULT;
> - goto out;
> - }
> - } else {
> - if (copy_to_user(buffer, buf, tsz)) {
> - ret = -EFAULT;
> - goto out;
> - }
> + if (_copy_to_user(buffer, (char *)start, tsz)) {
> + ret = -EFAULT;
> + goto out;
> }
> break;
> default:
> --
> 2.39.2
>
