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Date: Thu, 16 Oct 2014 15:33:55 +0200
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH v11 06/21] vfs: Add copy_to_iter(), copy_from_iter() and
iov_iter_zero()
On 25-Sep-2014 04:33:23 PM, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@...ux.intel.com>
>
> For DAX, we want to be able to copy between iovecs and kernel addresses
> that don't necessarily have a struct page. This is a fairly simple
> rearrangement for bvec iters to kmap the pages outside and pass them in,
> but for user iovecs it gets more complicated because we might try various
> different ways to kmap the memory. Duplicating the existing logic works
> out best in this case.
>
> We need to be able to write zeroes to an iovec for reads from unwritten
> ranges in a file. This is performed by the new iov_iter_zero() function,
> again patterned after the existing code that handles iovec iterators.
>
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> ---
> include/linux/uio.h | 3 +
> mm/iov_iter.c | 237 ++++++++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 226 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 48d64e6..1863ddd 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -80,6 +80,9 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
> struct iov_iter *i);
> size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
> struct iov_iter *i);
> +size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i);
> +size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
> +size_t iov_iter_zero(size_t bytes, struct iov_iter *);
> unsigned long iov_iter_alignment(const struct iov_iter *i);
> void iov_iter_init(struct iov_iter *i, int direction, const struct iovec *iov,
> unsigned long nr_segs, size_t count);
> diff --git a/mm/iov_iter.c b/mm/iov_iter.c
> index ab88dc0..d481fd8 100644
> --- a/mm/iov_iter.c
> +++ b/mm/iov_iter.c
> @@ -4,6 +4,96 @@
> #include <linux/slab.h>
> #include <linux/vmalloc.h>
>
> +static size_t copy_to_iter_iovec(void *from, size_t bytes, struct iov_iter *i)
> +{
> + size_t skip, copy, left, wanted;
> + const struct iovec *iov;
> + char __user *buf;
> +
> + if (unlikely(bytes > i->count))
> + bytes = i->count;
> +
> + if (unlikely(!bytes))
> + return 0;
> +
> + wanted = bytes;
> + iov = i->iov;
> + skip = i->iov_offset;
> + buf = iov->iov_base + skip;
> + copy = min(bytes, iov->iov_len - skip);
> +
> + left = __copy_to_user(buf, from, copy);
How comes this function uses __copy_to_user without any access_ok()
check ? This has security implications.
> + copy -= left;
> + skip += copy;
> + from += copy;
> + bytes -= copy;
> + while (unlikely(!left && bytes)) {
> + iov++;
> + buf = iov->iov_base;
> + copy = min(bytes, iov->iov_len);
> + left = __copy_to_user(buf, from, copy);
same here.
> + copy -= left;
> + skip = copy;
> + from += copy;
> + bytes -= copy;
> + }
> +
> + if (skip == iov->iov_len) {
> + iov++;
> + skip = 0;
> + }
> + i->count -= wanted - bytes;
> + i->nr_segs -= iov - i->iov;
> + i->iov = iov;
> + i->iov_offset = skip;
> + return wanted - bytes;
> +}
> +
> +static size_t copy_from_iter_iovec(void *to, size_t bytes, struct iov_iter *i)
> +{
> + size_t skip, copy, left, wanted;
> + const struct iovec *iov;
> + char __user *buf;
> +
> + if (unlikely(bytes > i->count))
> + bytes = i->count;
> +
> + if (unlikely(!bytes))
> + return 0;
> +
> + wanted = bytes;
> + iov = i->iov;
> + skip = i->iov_offset;
> + buf = iov->iov_base + skip;
> + copy = min(bytes, iov->iov_len - skip);
> +
> + left = __copy_from_user(to, buf, copy);
same here.
> + copy -= left;
> + skip += copy;
> + to += copy;
> + bytes -= copy;
> + while (unlikely(!left && bytes)) {
> + iov++;
> + buf = iov->iov_base;
> + copy = min(bytes, iov->iov_len);
> + left = __copy_from_user(to, buf, copy);
same.
> + copy -= left;
> + skip = copy;
> + to += copy;
> + bytes -= copy;
> + }
> +
> + if (skip == iov->iov_len) {
> + iov++;
> + skip = 0;
> + }
> + i->count -= wanted - bytes;
> + i->nr_segs -= iov - i->iov;
> + i->iov = iov;
> + i->iov_offset = skip;
> + return wanted - bytes;
> +}
> +
> static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
> struct iov_iter *i)
> {
> @@ -166,6 +256,50 @@ done:
> return wanted - bytes;
> }
>
> +static size_t zero_iovec(size_t bytes, struct iov_iter *i)
> +{
> + size_t skip, copy, left, wanted;
> + const struct iovec *iov;
> + char __user *buf;
> +
> + if (unlikely(bytes > i->count))
> + bytes = i->count;
> +
> + if (unlikely(!bytes))
> + return 0;
> +
> + wanted = bytes;
> + iov = i->iov;
> + skip = i->iov_offset;
> + buf = iov->iov_base + skip;
> + copy = min(bytes, iov->iov_len - skip);
> +
> + left = __clear_user(buf, copy);
I would guess an access_ok() would be needed here too.
> + copy -= left;
> + skip += copy;
> + bytes -= copy;
> +
> + while (unlikely(!left && bytes)) {
> + iov++;
> + buf = iov->iov_base;
> + copy = min(bytes, iov->iov_len);
> + left = __clear_user(buf, copy);
Same.
> + copy -= left;
> + skip = copy;
> + bytes -= copy;
> + }
> +
> + if (skip == iov->iov_len) {
> + iov++;
> + skip = 0;
> + }
> + i->count -= wanted - bytes;
> + i->nr_segs -= iov - i->iov;
> + i->iov = iov;
> + i->iov_offset = skip;
> + return wanted - bytes;
> +}
> +
> static size_t __iovec_copy_from_user_inatomic(char *vaddr,
> const struct iovec *iov, size_t base, size_t bytes)
> {
> @@ -412,12 +546,17 @@ static void memcpy_to_page(struct page *page, size_t offset, char *from, size_t
> kunmap_atomic(to);
> }
>
> -static size_t copy_page_to_iter_bvec(struct page *page, size_t offset, size_t bytes,
> - struct iov_iter *i)
> +static void memzero_page(struct page *page, size_t offset, size_t len)
> +{
> + char *addr = kmap_atomic(page);
> + memset(addr + offset, 0, len);
> + kunmap_atomic(addr);
> +}
> +
> +static size_t copy_to_iter_bvec(void *from, size_t bytes, struct iov_iter *i)
> {
> size_t skip, copy, wanted;
> const struct bio_vec *bvec;
> - void *kaddr, *from;
>
> if (unlikely(bytes > i->count))
> bytes = i->count;
> @@ -430,8 +569,6 @@ static size_t copy_page_to_iter_bvec(struct page *page, size_t offset, size_t by
> skip = i->iov_offset;
> copy = min_t(size_t, bytes, bvec->bv_len - skip);
>
> - kaddr = kmap_atomic(page);
> - from = kaddr + offset;
> memcpy_to_page(bvec->bv_page, skip + bvec->bv_offset, from, copy);
> skip += copy;
> from += copy;
> @@ -444,7 +581,6 @@ static size_t copy_page_to_iter_bvec(struct page *page, size_t offset, size_t by
> from += copy;
> bytes -= copy;
> }
> - kunmap_atomic(kaddr);
> if (skip == bvec->bv_len) {
> bvec++;
> skip = 0;
> @@ -456,12 +592,10 @@ static size_t copy_page_to_iter_bvec(struct page *page, size_t offset, size_t by
> return wanted - bytes;
> }
>
> -static size_t copy_page_from_iter_bvec(struct page *page, size_t offset, size_t bytes,
> - struct iov_iter *i)
> +static size_t copy_from_iter_bvec(void *to, size_t bytes, struct iov_iter *i)
> {
> size_t skip, copy, wanted;
> const struct bio_vec *bvec;
> - void *kaddr, *to;
>
> if (unlikely(bytes > i->count))
> bytes = i->count;
> @@ -473,10 +607,6 @@ static size_t copy_page_from_iter_bvec(struct page *page, size_t offset, size_t
> bvec = i->bvec;
> skip = i->iov_offset;
>
> - kaddr = kmap_atomic(page);
> -
> - to = kaddr + offset;
> -
> copy = min(bytes, bvec->bv_len - skip);
>
> memcpy_from_page(to, bvec->bv_page, bvec->bv_offset + skip, copy);
> @@ -493,7 +623,6 @@ static size_t copy_page_from_iter_bvec(struct page *page, size_t offset, size_t
> to += copy;
> bytes -= copy;
> }
> - kunmap_atomic(kaddr);
> if (skip == bvec->bv_len) {
> bvec++;
> skip = 0;
> @@ -505,6 +634,61 @@ static size_t copy_page_from_iter_bvec(struct page *page, size_t offset, size_t
> return wanted;
> }
>
> +static size_t copy_page_to_iter_bvec(struct page *page, size_t offset,
> + size_t bytes, struct iov_iter *i)
> +{
> + void *kaddr = kmap_atomic(page);
> + size_t wanted = copy_to_iter_bvec(kaddr + offset, bytes, i);
missing newline.
> + kunmap_atomic(kaddr);
> + return wanted;
> +}
> +
> +static size_t copy_page_from_iter_bvec(struct page *page, size_t offset,
> + size_t bytes, struct iov_iter *i)
> +{
> + void *kaddr = kmap_atomic(page);
> + size_t wanted = copy_from_iter_bvec(kaddr + offset, bytes, i);
missing newline.
Thanks,
Mathieu
> + kunmap_atomic(kaddr);
> + return wanted;
> +}
> +
> +static size_t zero_bvec(size_t bytes, struct iov_iter *i)
> +{
> + size_t skip, copy, wanted;
> + const struct bio_vec *bvec;
> +
> + if (unlikely(bytes > i->count))
> + bytes = i->count;
> +
> + if (unlikely(!bytes))
> + return 0;
> +
> + wanted = bytes;
> + bvec = i->bvec;
> + skip = i->iov_offset;
> + copy = min_t(size_t, bytes, bvec->bv_len - skip);
> +
> + memzero_page(bvec->bv_page, skip + bvec->bv_offset, copy);
> + skip += copy;
> + bytes -= copy;
> + while (bytes) {
> + bvec++;
> + copy = min(bytes, (size_t)bvec->bv_len);
> + memzero_page(bvec->bv_page, bvec->bv_offset, copy);
> + skip = copy;
> + bytes -= copy;
> + }
> + if (skip == bvec->bv_len) {
> + bvec++;
> + skip = 0;
> + }
> + i->count -= wanted - bytes;
> + i->nr_segs -= bvec - i->bvec;
> + i->bvec = bvec;
> + i->iov_offset = skip;
> + return wanted - bytes;
> +}
> +
> static size_t copy_from_user_bvec(struct page *page,
> struct iov_iter *i, unsigned long offset, size_t bytes)
> {
> @@ -668,6 +852,31 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
> }
> EXPORT_SYMBOL(copy_page_from_iter);
>
> +size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i)
> +{
> + if (i->type & ITER_BVEC)
> + return copy_to_iter_bvec(addr, bytes, i);
> + else
> + return copy_to_iter_iovec(addr, bytes, i);
> +}
> +
> +size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
> +{
> + if (i->type & ITER_BVEC)
> + return copy_from_iter_bvec(addr, bytes, i);
> + else
> + return copy_from_iter_iovec(addr, bytes, i);
> +}
> +
> +size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
> +{
> + if (i->type & ITER_BVEC) {
> + return zero_bvec(bytes, i);
> + } else {
> + return zero_iovec(bytes, i);
> + }
> +}
> +
> size_t iov_iter_copy_from_user_atomic(struct page *page,
> struct iov_iter *i, unsigned long offset, size_t bytes)
> {
> --
> 2.1.0
>
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>
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
Key fingerprint: 2A0B 4ED9 15F2 D3FA 45F5 B162 1728 0A97 8118 6ACF
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