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From: Randy Dunlap on 11 Aug 2010 19:50
On Wed, 11 Aug 2010 16:06:24 -0700 akpm(a)linux-foundation.org wrote:

>
> The patch titled
> drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> has been added to the -mm tree. Its filename is
> drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386.patch
>
> Before you just go and hit "reply", please:
> a) Consider who else should be cc'ed
> b) Prefer to cc a suitable mailing list as well
> c) Ideally: find the original patch on the mailing list and do a
> reply-to-all to that, adding suitable additional cc's
>
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
>
> See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
> out what to do about this
>
> The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
>
> ------------------------------------------------------
> Subject: drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> From: Andrew Morton <akpm(a)linux-foundation.org>
>
> Might be an x86 bug? A get_user() on a u64 on i386 expands to
>
> #define __get_user_8(__ret_gu, __val_gu, ptr) \
> __get_user_x(X, __ret_gu, __val_gu, ptr)
>
> which emits a call to __get_user_X(), which doesn't exist.
>
> Kludge around it with copy_from_user().
>

Reported and fixed yesterday.

>
>
> While we're there, teach it how to print size_t's:

That was also patched, but yours is better.
I missed the cast in Huang's patch.


> drivers/acpi/apei/erst-dbg.c: In function 'erst_dbg_read':
> drivers/acpi/apei/erst-dbg.c:106: warning: format '%lx' expects type 'long unsigned int', but argument 3 has type 'ssize_t'
>
> Cc: Glauber Costa <gcosta(a)redhat.com>
> Cc: Len Brown <lenb(a)kernel.org>
> Cc: Huang Ying <ying.huang(a)intel.com>
> Cc: "H. Peter Anvin" <hpa(a)zytor.com>
> Cc: Ingo Molnar <mingo(a)elte.hu>
> Cc: Thomas Gleixner <tglx(a)linutronix.de>
> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
> ---
>
> drivers/acpi/apei/erst-dbg.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff -puN drivers/acpi/apei/erst-dbg.c~drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386 drivers/acpi/apei/erst-dbg.c
> --- a/drivers/acpi/apei/erst-dbg.c~drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386
> +++ a/drivers/acpi/apei/erst-dbg.c
> @@ -57,9 +57,10 @@ static long erst_dbg_ioctl(struct file *
>
> switch (cmd) {
> case APEI_ERST_CLEAR_RECORD:
> - rc = get_user(record_id, (u64 __user *)arg);
> + rc = copy_from_user(&record_id, (const void __user *)arg,
> + sizeof(record_id));
> if (rc)
> - return rc;
> + return -EFAULT;
> return erst_clear(record_id);
> case APEI_ERST_GET_RECORD_COUNT:
> rc = erst_get_record_count();
> @@ -104,7 +105,7 @@ retry:
> goto out;
> if (len > ERST_DBG_RECORD_LEN_MAX) {
> pr_warning(ERST_DBG_PFX
> - "Record (ID: 0x%llx) length is too long: 0x%lx\n",
> + "Record (ID: 0x%llx) length is too long: 0x%zx\n",
> id, len);
> rc = -EIO;
> goto out;
> _


---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***
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From: Andrew Morton on 11 Aug 2010 20:40
On Wed, 11 Aug 2010 16:43:10 -0700 Randy Dunlap <randy.dunlap(a)oracle.com> wrote:

> On Wed, 11 Aug 2010 16:06:24 -0700 akpm(a)linux-foundation.org wrote:
>
> >
> > The patch titled
> > drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> > has been added to the -mm tree. Its filename is
> > drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386.patch
> >
> > Before you just go and hit "reply", please:
> > a) Consider who else should be cc'ed
> > b) Prefer to cc a suitable mailing list as well
> > c) Ideally: find the original patch on the mailing list and do a
> > reply-to-all to that, adding suitable additional cc's
> >
> > *** Remember to use Documentation/SubmitChecklist when testing your code ***
> >
> > See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
> > out what to do about this
> >
> > The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
> >
> > ------------------------------------------------------
> > Subject: drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> > From: Andrew Morton <akpm(a)linux-foundation.org>
> >
> > Might be an x86 bug? A get_user() on a u64 on i386 expands to
> >
> > #define __get_user_8(__ret_gu, __val_gu, ptr) \
> > __get_user_x(X, __ret_gu, __val_gu, ptr)
> >
> > which emits a call to __get_user_X(), which doesn't exist.
> >
> > Kludge around it with copy_from_user().
> >
>
> Reported and fixed yesterday.

Not very well.

+ rc = copy_from_user(&record_id, (void __user *)arg,
+ sizeof(u64));

better to use sizeof(record_id).

Where's Len??


Anyway, this should be fixed in x86 core, I suspect.
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From: Huang Ying on 11 Aug 2010 20:50
On Thu, 2010-08-12 at 08:33 +0800, Andrew Morton wrote:
> On Wed, 11 Aug 2010 16:43:10 -0700 Randy Dunlap <randy.dunlap(a)oracle.com> wrote:
>
> > On Wed, 11 Aug 2010 16:06:24 -0700 akpm(a)linux-foundation.org wrote:
> >
> > >
> > > The patch titled
> > > drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> > > has been added to the -mm tree. Its filename is
> > > drivers-acpi-apei-erst-dbgc-get_useru64-doesnt-work-on-i386.patch
> > >
> > > Before you just go and hit "reply", please:
> > > a) Consider who else should be cc'ed
> > > b) Prefer to cc a suitable mailing list as well
> > > c) Ideally: find the original patch on the mailing list and do a
> > > reply-to-all to that, adding suitable additional cc's
> > >
> > > *** Remember to use Documentation/SubmitChecklist when testing your code ***
> > >
> > > See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
> > > out what to do about this
> > >
> > > The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
> > >
> > > ------------------------------------------------------
> > > Subject: drivers/acpi/apei/erst-dbg.c: get_user(u64) doesn't work on i386
> > > From: Andrew Morton <akpm(a)linux-foundation.org>
> > >
> > > Might be an x86 bug? A get_user() on a u64 on i386 expands to
> > >
> > > #define __get_user_8(__ret_gu, __val_gu, ptr) \
> > > __get_user_x(X, __ret_gu, __val_gu, ptr)
> > >
> > > which emits a call to __get_user_X(), which doesn't exist.
> > >
> > > Kludge around it with copy_from_user().
> > >
> >
> > Reported and fixed yesterday.
>
> Not very well.
>
> + rc = copy_from_user(&record_id, (void __user *)arg,
> + sizeof(u64));
>
> better to use sizeof(record_id).

Will fix this with a new version. And the ssize printk format string.

> Where's Len??
>
> Anyway, this should be fixed in x86 core, I suspect.

Yes. I think so too.

Best Regards,
Huang Ying


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From: Andrew Morton on 12 Aug 2010 00:40
On Wed, 11 Aug 2010 21:22:51 -0700 "H. Peter Anvin" <hpa(a)zytor.com> wrote:

> [Adding Linux and linux-arch. The context is that get_user/put_user
> don't work on 64 bit values on i386.]
>
> On 08/11/2010 05:33 PM, Andrew Morton wrote:
> >
> > Anyway, this should be fixed in x86 core, I suspect.
>
> After looking at it -- and suffering a bad case of d__j__ vu -- I'm
> reluctant to change it, as get/put_user are specified to work only on
> locally atomic data:
>
> * This macro copies a single simple variable from user space to kernel
> * space. It supports simple types like char and int, but not larger
> * data types like structures or arrays.
>
> Given that u64 is not a simple type on 32 bits, it would appear that the
> behavior is intentional.
>
> A user might very well find that supporting u64 and/or structure types
> would be beneficial, but it would a) be a semantic change, and b) would
> introduce the possibility of a partially completed transfer. That is a
> semantic change to the interface. However, it may very well be nicer to
> have a generally available get_user()/put_user() for the cases which
> would just kick an EFAULT up the stack when they fail anyway.
>
> If there is consensus for making get_user/put_user a general interface,
> I'm more than willing to do the x86 changes, but I don't want to do them
> a) unilaterally and b) for 2.6.36. This seems like .37 material at this
> point.

It occurs so rarely that it's probably not worth bothering about, IMO.

However we should arrange for it to fail at compile time rather than
at link time, please.



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From: Andrew Morton on 12 Aug 2010 02:10
On Wed, 11 Aug 2010 22:06:08 -0700 "H. Peter Anvin" <hpa(a)zytor.com> wrote:

> On 08/11/2010 09:30 PM, Andrew Morton wrote:
> >
> > It occurs so rarely that it's probably not worth bothering about, IMO.
> >
>
> I think the real question is if we want people to convert:
>
> if (copy_from_user(foo, bar, sizeof *foo))
> return -EFAULT;
>
> ... into ...
>
> if (get_user(*foo, bar))
> return -EFAULT;
>
> ... or ...
>
> rv = get_user(*foo, bar);
> if (rv)
> return rv;
>
> ... where *foo is a structure type. It does have the advantage that a
> single API does everything, simple or not, but has the disadvantage that
> the partial-access semantics are now less explicit.
>

Well, anyone who does get_user() on a struct while expecting it to be
atomic gets to own both pieces. I think the problem here is
specifically u64/s64. These work on 64-bit but don't work on 32-bit.

Is the atomicity really a problem? If userspace updates the 64-bit
number while the kernel is copying it, the kernel gets a garbage
number. But so what? Userspace can feed the kernel garbage numbers in
lots of ways, and the kernel must be able to cope with it
appropriately.


<I suspect you can do get_user() on a 4-byte or 8-byte struct right now
and it'll work>
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