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From: Al Viro <viro@zeniv.linux.org.uk>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: cluster-devel@redhat.com, Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v7 03/19] gup: Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable}
Date: Fri, 27 Aug 2021 19:08:34 +0000	[thread overview]
Message-ID: <YSk4Mvbyp8lxPfPF@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <20210827164926.1726765-4-agruenba@redhat.com>

On Fri, Aug 27, 2021 at 06:49:10PM +0200, Andreas Gruenbacher wrote:
> Turn fault_in_pages_{readable,writeable} into versions that return the
> number of bytes not faulted in (similar to copy_to_user) instead of
> returning a non-zero value when any of the requested pages couldn't be
> faulted in.  This supports the existing users that require all pages to
> be faulted in as well as new users that are happy if any pages can be
> faulted in at all.
> 
> Neither of these functions is entirely trivial and it doesn't seem
> useful to inline them, so move them to mm/gup.c.
> 
> Rename the functions to fault_in_{readable,writeable} to make sure that
> this change doesn't silently break things.

I'm sorry, but this is wrong.  The callers need to be reviewed and
sanitized.  You have several oddball callers (most of them simply
wrong) *and* the ones on a very hot path in write(2).  And _there_
the existing behaviour does the wrong thing for memory poisoning setups.

	Do we have *any* cases where we both need the fault-in at all *and*
would not be better off with "fail only if the first byte couldn't have been
faulted in"?

> diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
> index 0608581967f0..38c3eae40c14 100644
> --- a/arch/powerpc/kernel/signal_32.c
> +++ b/arch/powerpc/kernel/signal_32.c
> @@ -1048,7 +1048,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
>  	if (new_ctx == NULL)
>  		return 0;
>  	if (!access_ok(new_ctx, ctx_size) ||
> -	    fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
> +	    fault_in_readable((char __user *)new_ctx, ctx_size))
>  		return -EFAULT;

This is completely pointless.  Look at do_setcontext() there.  Seriously,
it immediately does
        if (!user_read_access_begin(ucp, sizeof(*ucp)))
			return -EFAULT;
so this access_ok() is so much garbage.  Then it does normal unsage_get_...()
stuff, so it doesn't need that fault-in crap at all - it *must* handle
copyin failures, fault-in or not.  Just lose that fault_in_... call and be
done with that.


> @@ -1237,7 +1237,7 @@ SYSCALL_DEFINE3(debug_setcontext, struct ucontext __user *, ctx,
>  #endif
>  
>  	if (!access_ok(ctx, sizeof(*ctx)) ||
> -	    fault_in_pages_readable((u8 __user *)ctx, sizeof(*ctx)))
> +	    fault_in_readable((char __user *)ctx, sizeof(*ctx)))
>  		return -EFAULT;

Ditto.

> diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> index 1831bba0582e..9f471b4a11e3 100644
> --- a/arch/powerpc/kernel/signal_64.c
> +++ b/arch/powerpc/kernel/signal_64.c
> @@ -688,7 +688,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
>  	if (new_ctx == NULL)
>  		return 0;
>  	if (!access_ok(new_ctx, ctx_size) ||
> -	    fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
> +	    fault_in_readable((char __user *)new_ctx, ctx_size))
>  		return -EFAULT;

... and again.

> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 0ba98e08a029..9233ecc31e2e 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2244,9 +2244,8 @@ static noinline int search_ioctl(struct inode *inode,
>  	key.offset = sk->min_offset;
>  
>  	while (1) {
> -		ret = fault_in_pages_writeable(ubuf + sk_offset,
> -					       *buf_size - sk_offset);
> -		if (ret)
> +		ret = -EFAULT;
> +		if (fault_in_writeable(ubuf + sk_offset, *buf_size - sk_offset))
>  			break;

Really?

> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 25dfc48536d7..069cedd9d7b4 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -191,7 +191,7 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
>  	buf = iov->iov_base + skip;
>  	copy = min(bytes, iov->iov_len - skip);
>  
> -	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_writeable(buf, copy)) {
> +	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_writeable(buf, copy)) {

Here we definitely want "fail only if nothing could be faulted in"

>  		kaddr = kmap_atomic(page);
>  		from = kaddr + offset;
>  
> @@ -275,7 +275,7 @@ static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t
>  	buf = iov->iov_base + skip;
>  	copy = min(bytes, iov->iov_len - skip);
>  
> -	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_pages_readable(buf, copy)) {
> +	if (IS_ENABLED(CONFIG_HIGHMEM) && !fault_in_readable(buf, copy)) {

Same.

> @@ -446,13 +446,11 @@ int iov_iter_fault_in_readable(const struct iov_iter *i, size_t bytes)
>  			bytes = i->count;
>  		for (p = i->iov, skip = i->iov_offset; bytes; p++, skip = 0) {
>  			size_t len = min(bytes, p->iov_len - skip);
> -			int err;
>  
>  			if (unlikely(!len))
>  				continue;
> -			err = fault_in_pages_readable(p->iov_base + skip, len);
> -			if (unlikely(err))
> -				return err;
> +			if (fault_in_readable(p->iov_base + skip, len))
> +				return -EFAULT;

... and the same, except that here we want failure only if nothing had already
been faulted in.

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  reply	other threads:[~2021-08-27 19:15 UTC|newest]

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 16:49 [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 01/19] iov_iter: Fix iov_iter_get_pages{, _alloc} page fault return value Andreas Gruenbacher
2021-09-09 11:09   ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 03/19] gup: Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-08-27 19:08   ` Al Viro [this message]
2021-09-03 14:56   ` Filipe Manana
2021-09-28 15:02     ` Andreas Gruenbacher
2021-09-28 16:37       ` Matthew Wilcox
2021-09-28 20:41         ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 04/19] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-27 18:53   ` Al Viro
2021-08-27 18:57     ` Linus Torvalds
2021-08-27 19:16       ` Al Viro
2021-08-27 20:56   ` Kari Argillander
2021-08-28 17:13     ` Linus Torvalds
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-27 18:49   ` Al Viro
2021-08-27 19:05     ` Linus Torvalds
2021-08-27 19:23       ` Al Viro
2021-08-27 19:33         ` Linus Torvalds
2021-08-27 19:37           ` Al Viro
2021-08-27 21:48             ` Al Viro
2021-08-27 21:57               ` Al Viro
2021-08-27 23:22                 ` Luck, Tony
2021-08-28  2:20                   ` Luck, Tony
2021-08-28 21:47                   ` Thomas Gleixner
2021-08-28 22:04                     ` Al Viro
2021-08-28 22:11                       ` Al Viro
2021-08-28 22:19                         ` Al Viro
2021-08-28 22:51                           ` Al Viro
2021-08-29 18:44                             ` Thomas Gleixner
2021-08-29 19:46                               ` Al Viro
2021-08-29 19:51                                 ` Thomas Gleixner
2021-08-28 22:20                         ` Tony Luck
2021-08-29  1:40                           ` Matthew Wilcox
2021-08-30 15:41                             ` Luck, Tony
2021-08-28 22:23                       ` Thomas Gleixner
2021-08-28 19:28               ` [Ocfs2-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl() Al Viro
2021-08-31 13:54                 ` Catalin Marinas
2021-08-31 15:28                   ` Al Viro
2021-08-31 16:01                     ` Catalin Marinas
2021-10-11 17:37                     ` Catalin Marinas
2021-10-11 19:15                       ` Linus Torvalds
2021-10-11 21:08                         ` Catalin Marinas
2021-10-11 23:59                           ` Linus Torvalds
2021-10-12 17:27                             ` Catalin Marinas
2021-10-12 17:58                               ` Linus Torvalds
2021-10-18 17:13                                 ` Catalin Marinas
2021-10-21  0:46                             ` Andreas Gruenbacher
2021-10-21 10:05                               ` Catalin Marinas
2021-10-21 14:42                                 ` Andreas Gruenbacher
2021-10-21 17:09                                   ` Catalin Marinas
2021-10-21 18:00                                     ` Andreas Gruenbacher
2021-10-22 18:41                                       ` Catalin Marinas
2021-10-25 19:37                                         ` Andreas Gruenbacher
2021-10-22  2:30                                   ` Linus Torvalds
2021-10-22  9:34                                     ` Catalin Marinas
2021-08-29  0:58               ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Al Viro
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 12/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 13/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 14/19] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-09-03 18:54   ` Darrick J. Wong
2021-09-09 11:17   ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-09-03 18:54   ` Darrick J. Wong
2021-09-09 11:20   ` Christoph Hellwig
2021-09-28 15:05     ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 16/19] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-27 18:30   ` Darrick J. Wong
2021-08-27 20:15     ` Andreas Gruenbacher
2021-08-27 21:32       ` Darrick J. Wong
2021-08-27 21:49         ` Andreas Grünbacher
2021-08-27 22:35         ` Linus Torvalds
2021-09-03 18:47           ` Darrick J. Wong
2021-09-03 18:53   ` Darrick J. Wong
2021-09-09 11:30   ` Christoph Hellwig
2021-09-09 17:22     ` Linus Torvalds
2021-09-10  7:36       ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 17/19] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-09-09 11:36   ` Christoph Hellwig
2021-09-09 17:17     ` Linus Torvalds
2021-09-10  7:24       ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 18/19] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-08-27 18:47   ` Al Viro
2021-08-27 19:56     ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 19/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-27 17:16 ` [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-09-01 19:52   ` Andreas Gruenbacher
2021-09-03 15:52     ` Linus Torvalds
2021-09-03 18:25       ` Al Viro
2021-09-03 18:47         ` Linus Torvalds
2021-09-03 19:51       ` Andreas Grünbacher
2021-09-03 15:07 ` Filipe Manana

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