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RE: [PATCH] xen/gnttab: fix gnttab_acquire_resource()
- To: Juergen Gross <jgross@xxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Fri, 9 Sep 2022 09:28:00 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 09 Sep 2022 09:28:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHYxCOLeMow4nnAdEmRQz42iuSBI63W0QoAgAADAYCAAABeMA==
- Thread-topic: [PATCH] xen/gnttab: fix gnttab_acquire_resource()
Kind regards,
Henry
> -----Original Message-----
> From: Juergen Gross <jgross@xxxxxxxx>
> Sent: Friday, September 9, 2022 5:26 PM
> To: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Henry Wang <Henry.Wang@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>;
> Julien Grall <julien@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> Wei Liu <wl@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH] xen/gnttab: fix gnttab_acquire_resource()
>
> On 09.09.22 11:15, Jan Beulich wrote:
> > On 09.09.2022 10:09, Juergen Gross wrote:
> >> Commit 9dc46386d89d ("gnttab: work around "may be used uninitialized"
> >> warning") was wrong, as vaddr can legitimately be NULL in case
> >> XENMEM_resource_grant_table_id_status was specified for a grant table
> >> v1. This would result in crashes in debug builds due to
> >> ASSERT_UNREACHABLE() triggering.
> >>
> >> Basically revert said commit, but keep returning -ENODATA in that case.
> >>
> >> Fixes: 9dc46386d89d ("gnttab: work around "may be used uninitialized"
> warning")
> >> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> >> ---
> >> Might be considered for 4.17 and for backporting
> >> ---
> >> xen/common/grant_table.c | 14 +++-----------
> >> 1 file changed, 3 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> >> index ad773a6996..68e7f1df38 100644
> >> --- a/xen/common/grant_table.c
> >> +++ b/xen/common/grant_table.c
> >> @@ -4125,7 +4125,10 @@ int gnttab_acquire_resource(
> >>
> >> case XENMEM_resource_grant_table_id_status:
> >> if ( gt->gt_version != 2 )
> >> + {
> >> + rc = -ENODATA;
> >> break;
> >> + }
> >
> > This path is supposed to produce -EINVAL.
>
> Okay.
>
> >
> >> @@ -4135,17 +4138,6 @@ int gnttab_acquire_resource(
> >> break;
> >> }
> >>
> >> - /*
> >> - * Some older toolchains can't spot that vaddrs won't remain
> uninitialized
> >> - * on non-error paths, and hence it needs setting to NULL at the top
> >> of
> the
> >> - * function. Leave some runtime safety.
> >> - */
> >> - if ( !vaddrs )
> >
> > I guess this wants amending by "&& !rc"?
>
> I can do that, if you like that better.
>
>
> Juergen
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