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Message-ID: <070237be-48a2-4a04-bc19-7217b68c8bcf@lucifer.local>
Date: Wed, 22 Mar 2023 06:17:24 +0000
From: Lorenzo Stoakes <lstoakes@...il.com>
To: Baoquan He <bhe@...hat.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()
On Wed, Mar 22, 2023 at 09:15:48AM +0800, Baoquan He wrote:
> 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?
>
Apologies, I didn't update the commit message after the latest revision! We
can just drop this sentence altogether.
Andrew - could you change the commit message to simply read:-
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.
Thanks!
> >
> > 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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