From: Greg KH <[email protected]>
To: David Hildenbrand <[email protected]>
Cc: David Laight <[email protected]>,
Al Viro <[email protected]>,
Nick Desaulniers <[email protected]>,
Christoph Hellwig <[email protected]>,
"[email protected]" <[email protected]>,
Andrew Morton <[email protected]>,
Jens Axboe <[email protected]>, Arnd Bergmann <[email protected]>,
David Howells <[email protected]>,
"[email protected]"
<[email protected]>,
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<[email protected]>
Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"
Date: Thu, 22 Oct 2020 14:57:59 +0200 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On Thu, Oct 22, 2020 at 02:42:24PM +0200, David Hildenbrand wrote:
> On 22.10.20 14:18, Greg KH wrote:
> > On Thu, Oct 22, 2020 at 12:48:05PM +0200, Greg KH wrote:
> >> On Thu, Oct 22, 2020 at 11:36:40AM +0200, David Hildenbrand wrote:
> >>> On 22.10.20 11:32, David Laight wrote:
> >>>> From: David Hildenbrand
> >>>>> Sent: 22 October 2020 10:25
> >>>> ...
> >>>>> ... especially because I recall that clang and gcc behave slightly
> >>>>> differently:
> >>>>>
> >>>>> https://github.com/hjl-tools/x86-psABI/issues/2
> >>>>>
> >>>>> "Function args are different: narrow types are sign or zero extended to
> >>>>> 32 bits, depending on their type. clang depends on this for incoming
> >>>>> args, but gcc doesn't make that assumption. But both compilers do it
> >>>>> when calling, so gcc code can call clang code.
> >>>>
> >>>> It really is best to use 'int' (or even 'long') for all numeric
> >>>> arguments (and results) regardless of the domain of the value.
> >>>>
> >>>> Related, I've always worried about 'bool'....
> >>>>
> >>>>> The upper 32 bits of registers are always undefined garbage for types
> >>>>> smaller than 64 bits."
> >>>>
> >>>> On x86-64 the high bits are zeroed by all 32bit loads.
> >>>
> >>> Yeah, but does not help here.
> >>>
> >>>
> >>> My thinking: if the compiler that calls import_iovec() has garbage in
> >>> the upper 32 bit
> >>>
> >>> a) gcc will zero it out and not rely on it being zero.
> >>> b) clang will not zero it out, assuming it is zero.
> >>>
> >>> But
> >>>
> >>> a) will zero it out when calling the !inlined variant
> >>> b) clang will zero it out when calling the !inlined variant
> >>>
> >>> When inlining, b) strikes. We access garbage. That would mean that we
> >>> have calling code that's not generated by clang/gcc IIUC.
> >>>
> >>> We can test easily by changing the parameters instead of adding an "inline".
> >>
> >> Let me try that as well, as I seem to have a good reproducer, but it
> >> takes a while to run...
> >
> > Ok, that didn't work.
> >
> > And I can't seem to "fix" this by adding noinline to patches further
> > along in the patch series (because this commit's function is no longer
> > present due to later patches.)
>
> We might have the same issues with iovec_from_user() and friends now.
>
> >
> > Will keep digging...
> >
> > greg k-h
> >
>
>
> Might be worth to give this a try, just to see if it's related to
> garbage in upper 32 bit and the way clang is handling it (might be a BUG
> in clang, though):
>
>
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 72d88566694e..7527298c6b56 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -267,7 +267,7 @@ size_t hash_and_copy_to_iter(const void *addr,
> size_t bytes, void *hashp,
> struct iov_iter *i);
>
> struct iovec *iovec_from_user(const struct iovec __user *uvector,
> - unsigned long nr_segs, unsigned long fast_segs,
> + unsigned nr_segs, unsigned fast_segs,
> struct iovec *fast_iov, bool compat);
> ssize_t import_iovec(int type, const struct iovec __user *uvec,
> unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 1635111c5bd2..58417f1916dc 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1652,7 +1652,7 @@ const void *dup_iter(struct iov_iter *new, struct
> iov_iter *old, gfp_t flags)
> EXPORT_SYMBOL(dup_iter);
>
> static int copy_compat_iovec_from_user(struct iovec *iov,
> - const struct iovec __user *uvec, unsigned long nr_segs)
> + const struct iovec __user *uvec, unsigned nr_segs)
> {
> const struct compat_iovec __user *uiov =
> (const struct compat_iovec __user *)uvec;
> @@ -1684,7 +1684,7 @@ static int copy_compat_iovec_from_user(struct
> iovec *iov,
> }
>
> static int copy_iovec_from_user(struct iovec *iov,
> - const struct iovec __user *uvec, unsigned long nr_segs)
> + const struct iovec __user *uvec, unsigned nr_segs)
> {
> unsigned long seg;
>
> @@ -1699,7 +1699,7 @@ static int copy_iovec_from_user(struct iovec *iov,
> }
>
> struct iovec *iovec_from_user(const struct iovec __user *uvec,
> - unsigned long nr_segs, unsigned long fast_segs,
> + unsigned nr_segs, unsigned fast_segs,
> struct iovec *fast_iov, bool compat)
> {
> struct iovec *iov = fast_iov;
> @@ -1738,7 +1738,7 @@ ssize_t __import_iovec(int type, const struct
> iovec __user *uvec,
> struct iov_iter *i, bool compat)
> {
> ssize_t total_len = 0;
> - unsigned long seg;
> + unsigned seg;
> struct iovec *iov;
>
> iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
>
Ah, I tested the other way around, making everything "unsigned long"
instead. Will go try this too, as other tests are still running...
thanks,
greg k-h
next prev parent reply other threads:[~2020-10-22 12:57 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-25 4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25 4:51 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-25 4:51 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-10-21 16:13 ` Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" Greg KH
2020-10-21 20:59 ` David Laight
2020-10-21 23:39 ` Al Viro
2020-10-22 8:26 ` Greg KH
2020-10-22 8:35 ` David Hildenbrand
2020-10-22 8:40 ` David Laight
2020-10-22 8:48 ` David Hildenbrand
2020-10-22 9:01 ` Greg KH
2020-10-22 9:06 ` David Laight
2020-10-22 9:19 ` David Hildenbrand
2020-10-22 9:25 ` David Hildenbrand
2020-10-22 9:32 ` David Laight
2020-10-22 9:36 ` David Hildenbrand
2020-10-22 10:48 ` Greg KH
2020-10-22 12:18 ` Greg KH
2020-10-22 12:42 ` David Hildenbrand
2020-10-22 12:57 ` Greg KH [this message]
2020-10-22 13:50 ` Greg KH
[not found] ` <CAK8P3a1B7OVdyzW0-97JwzZiwp0D0fnSfyete16QTvPp_1m07A@mail.gmail.com>
2020-10-22 14:40 ` Greg KH
2020-10-22 16:15 ` David Laight
2020-10-23 12:46 ` David Laight
2020-10-23 13:09 ` David Hildenbrand
2020-10-23 14:33 ` David Hildenbrand
2020-10-23 14:39 ` David Laight
2020-10-23 14:47 ` 'Greg KH'
2020-10-23 16:33 ` David Hildenbrand
2020-11-02 9:06 ` David Laight
2020-11-02 13:52 ` 'Greg KH'
2020-11-02 18:23 ` David Laight
2020-10-23 17:58 ` Al Viro
2020-10-23 18:27 ` Segher Boessenkool
2020-10-23 21:28 ` David Laight
2020-10-24 17:29 ` Segher Boessenkool
2020-10-24 21:12 ` David Laight
[not found] ` <CAK8P3a1n+b8hOMhNQSDzgic03dyXbmpccfTJ3C1bGKvzsgMXbg@mail.gmail.com>
2020-10-23 13:28 ` David Laight
2020-10-22 13:23 ` Christoph Hellwig
2020-10-22 16:35 ` David Laight
2020-10-22 16:40 ` Matthew Wilcox
2020-10-22 16:50 ` David Laight
2020-10-22 17:00 ` Nick Desaulniers
2020-10-22 20:59 ` Eric Biggers
2020-10-22 21:28 ` Al Viro
2020-10-22 18:19 ` Al Viro
2020-10-22 17:54 ` Nick Desaulniers
[not found] ` <CAK8P3a3LjG+ZvmQrkb9zpgov8xBkQQWrkHBPgjfYSqBKGrwT4w@mail.gmail.com>
2020-10-22 19:04 ` Nick Desaulniers
2020-10-22 19:24 ` Al Viro
2020-10-22 19:27 ` Al Viro
2020-10-22 20:06 ` Al Viro
2020-10-22 20:09 ` Al Viro
2020-10-22 20:11 ` Nick Desaulniers
2020-10-22 22:07 ` David Laight
2020-10-23 13:12 ` David Hildenbrand
2020-10-22 22:04 ` David Laight
2020-10-22 9:28 ` David Laight
2020-10-22 9:02 ` David Laight
2020-09-25 4:51 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-25 4:51 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-25 4:51 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-25 4:51 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-25 4:51 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-25 4:51 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-25 4:51 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-25 15:23 ` let import_iovec deal with compat_iovecs as well v4 Al Viro
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