On 07/31/23 at 10:50pm, 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.
> */
> - 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,
> };
On 6.5-rc4, the failures can be reproduced stably on a arm64 machine.
With patch applied, both makedumpfile and objdump test cases passed.
And the code change looks good to me, thanks.
Tested-by: Baoquan He <bhe@xxxxxxxxxx>
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
===============================================
[root@ ~]# makedumpfile --mem-usage /proc/kcore
The kernel version is not supported.
The makedumpfile operation may be incomplete.
TYPE PAGES EXCLUDABLE DESCRIPTION
----------------------------------------------------------------------
ZERO 76234 yes Pages filled with zero
NON_PRI_CACHE 147613 yes Cache pages without private flag
PRI_CACHE 3847 yes Cache pages with private flag
USER 15276 yes User process pages
FREE 15809884 yes Free pages
KERN_DATA 459950 no Dumpable kernel data
page size: 4096
Total pages on system: 16512804
Total size on system: 67636445184 Byte
[root@ ~]# objdump -d --start-address=0x^C
[root@ ~]# cat /proc/kallsyms | grep ksys_read
ffffab3be77229d8 T ksys_readahead
ffffab3be782a700 T ksys_read
[root@ ~]# objdump -d --start-address=0xffffab3be782a700 --stop-address=0xffffab3be782a710 /proc/kcore
/proc/kcore: file format elf64-littleaarch64
Disassembly of section load1:
ffffab3be782a700 <load1+0x41a700>:
ffffab3be782a700: aa1e03e9 mov x9, x30
ffffab3be782a704: d503201f nop
ffffab3be782a708: d503233f paciasp
ffffab3be782a70c: a9bc7bfd stp x29, x30, [sp, #-64]!
objdump: error: /proc/kcore(load2) is too large (0x7bff70000000 bytes)
objdump: Reading section load2 failed because: memory exhausted
