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Message-ID: <ZBpWxI+LYiwasnvj@MiWiFi-R3L-srv>
Date: Wed, 22 Mar 2023 09:15:48 +0800
From: Baoquan He <bhe@...hat.com>
To: Lorenzo Stoakes <lstoakes@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Uladzislau Rezki <urezki@...il.com>,
Matthew Wilcox <willy@...radead.org>,
David Hildenbrand <david@...hat.com>,
Liu Shixin <liushixin2@...wei.com>,
Jiri Olsa <jolsa@...nel.org>, Jens Axboe <axboe@...nel.dk>,
Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v4 2/4] fs/proc/kcore: convert read_kcore() to
read_kcore_iter()
Hi Lorenzo,
On 03/21/23 at 08:54pm, Lorenzo Stoakes wrote:
> Now we have eliminated spinlocks from the vread() case, convert
> read_kcore() to read_kcore_iter().
Sorry for late comment.
Here I could miss something important, I don't get where we have
eliminated spinlocks from the vread() case. Do I misunderstand this
sentence?
>
> For the time being we still use a bounce buffer for vread(), however in the
> next patch we will convert this to interact directly with the iterator and
> eliminate the bounce buffer altogether.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---
> fs/proc/kcore.c | 58 ++++++++++++++++++++++++-------------------------
> 1 file changed, 29 insertions(+), 29 deletions(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 556f310d6aa4..25e0eeb8d498 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -24,7 +24,7 @@
> #include <linux/memblock.h>
> #include <linux/init.h>
> #include <linux/slab.h>
> -#include <linux/uaccess.h>
> +#include <linux/uio.h>
> #include <asm/io.h>
> #include <linux/list.h>
> #include <linux/ioport.h>
> @@ -308,9 +308,12 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
> }
>
> static ssize_t
> -read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> +read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
> {
> + struct file *file = iocb->ki_filp;
> char *buf = file->private_data;
> + loff_t *ppos = &iocb->ki_pos;
> +
> size_t phdrs_offset, notes_offset, data_offset;
> size_t page_offline_frozen = 1;
> size_t phdrs_len, notes_len;
> @@ -318,6 +321,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> size_t tsz;
> int nphdr;
> unsigned long start;
> + size_t buflen = iov_iter_count(iter);
> size_t orig_buflen = buflen;
> int ret = 0;
>
> @@ -333,7 +337,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> notes_offset = phdrs_offset + phdrs_len;
>
> /* ELF file header. */
> - if (buflen && *fpos < sizeof(struct elfhdr)) {
> + if (buflen && *ppos < sizeof(struct elfhdr)) {
> struct elfhdr ehdr = {
> .e_ident = {
> [EI_MAG0] = ELFMAG0,
> @@ -355,19 +359,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> .e_phnum = nphdr,
> };
>
> - tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
> - if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
> + tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *ppos);
> + if (copy_to_iter((char *)&ehdr + *ppos, tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
>
> - buffer += tsz;
> buflen -= tsz;
> - *fpos += tsz;
> + *ppos += tsz;
> }
>
> /* ELF program headers. */
> - if (buflen && *fpos < phdrs_offset + phdrs_len) {
> + if (buflen && *ppos < phdrs_offset + phdrs_len) {
> struct elf_phdr *phdrs, *phdr;
>
> phdrs = kzalloc(phdrs_len, GFP_KERNEL);
> @@ -397,22 +400,21 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> phdr++;
> }
>
> - tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
> - if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
> - tsz)) {
> + tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *ppos);
> + if (copy_to_iter((char *)phdrs + *ppos - phdrs_offset, tsz,
> + iter) != tsz) {
> kfree(phdrs);
> ret = -EFAULT;
> goto out;
> }
> kfree(phdrs);
>
> - buffer += tsz;
> buflen -= tsz;
> - *fpos += tsz;
> + *ppos += tsz;
> }
>
> /* ELF note segment. */
> - if (buflen && *fpos < notes_offset + notes_len) {
> + if (buflen && *ppos < notes_offset + notes_len) {
> struct elf_prstatus prstatus = {};
> struct elf_prpsinfo prpsinfo = {
> .pr_sname = 'R',
> @@ -447,24 +449,23 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> vmcoreinfo_data,
> min(vmcoreinfo_size, notes_len - i));
>
> - tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
> - if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
> + tsz = min_t(size_t, buflen, notes_offset + notes_len - *ppos);
> + if (copy_to_iter(notes + *ppos - notes_offset, tsz, iter) != tsz) {
> kfree(notes);
> ret = -EFAULT;
> goto out;
> }
> kfree(notes);
>
> - buffer += tsz;
> buflen -= tsz;
> - *fpos += tsz;
> + *ppos += tsz;
> }
>
> /*
> * Check to see if our file offset matches with any of
> * the addresses in the elf_phdr on our list.
> */
> - start = kc_offset_to_vaddr(*fpos - data_offset);
> + start = kc_offset_to_vaddr(*ppos - data_offset);
> if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
> tsz = buflen;
>
> @@ -497,7 +498,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> }
>
> if (!m) {
> - if (clear_user(buffer, tsz)) {
> + if (iov_iter_zero(tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> @@ -508,14 +509,14 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> case KCORE_VMALLOC:
> vread(buf, (char *)start, tsz);
> /* we have to zero-fill user buffer even if no read */
> - if (copy_to_user(buffer, buf, tsz)) {
> + if (copy_to_iter(buf, tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> break;
> case KCORE_USER:
> /* User page is handled prior to normal kernel page: */
> - if (copy_to_user(buffer, (char *)start, tsz)) {
> + if (copy_to_iter((char *)start, tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> @@ -531,7 +532,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> */
> if (!page || PageOffline(page) ||
> is_page_hwpoison(page) || !pfn_is_ram(pfn)) {
> - if (clear_user(buffer, tsz)) {
> + if (iov_iter_zero(tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> @@ -541,25 +542,24 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> case KCORE_VMEMMAP:
> case KCORE_TEXT:
> /*
> - * We use _copy_to_user() to bypass usermode hardening
> + * We use _copy_to_iter() to bypass usermode hardening
> * which would otherwise prevent this operation.
> */
> - if (_copy_to_user(buffer, (char *)start, tsz)) {
> + if (_copy_to_iter((char *)start, tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> break;
> default:
> pr_warn_once("Unhandled KCORE type: %d\n", m->type);
> - if (clear_user(buffer, tsz)) {
> + if (iov_iter_zero(tsz, iter) != tsz) {
> ret = -EFAULT;
> goto out;
> }
> }
> skip:
> buflen -= tsz;
> - *fpos += tsz;
> - buffer += tsz;
> + *ppos += tsz;
> start += tsz;
> tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
> }
> @@ -603,7 +603,7 @@ static int release_kcore(struct inode *inode, struct file *file)
> }
>
> static const struct proc_ops kcore_proc_ops = {
> - .proc_read = read_kcore,
> + .proc_read_iter = read_kcore_iter,
> .proc_open = open_kcore,
> .proc_release = release_kcore,
> .proc_lseek = default_llseek,
> --
> 2.39.2
>
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