Re: [PATCH 1/3] kexec_file: fix incorrect end value passed to kimage_is_destination_range()

From: Baoquan He <bhe@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Yuntao Wang <ytcoode@gmail.com>,
	linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
	x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH 1/3] kexec_file: fix incorrect end value passed to kimage_is_destination_range()
Date: Sat, 16 Dec 2023 10:21:53 +0800	[thread overview]
Message-ID: <ZX0JwbQ59XH5rqm9@MiWiFi-R3L-srv> (raw)
In-Reply-To: <87a5qb4avf.fsf@email.froward.int.ebiederm.org>

On 12/15/23 at 11:46am, Eric W. Biederman wrote:
> Yuntao Wang <ytcoode@gmail.com> writes:
> 
> > The end parameter received by kimage_is_destination_range() should be the
> > last valid byte address of the target memory segment plus 1. However, in
> > the locate_mem_hole_bottom_up() and locate_mem_hole_top_down() functions,
> > the corresponding value passed to kimage_is_destination_range() is the last
> > valid byte address of the target memory segment, which is 1 less. Fix
> > it.
> 
> If that is true we I think we should rather fix
> kimage_is_destination_range.

It's true wit the current implementation of
kimage_is_destination_range(). Its callers pass the start/end+1
pair. Agree we should fix kimage_is_destination_range() instead and
adjust callers, such as kimage_alloc_normal_control_pages(), and
kimage_alloc_page().

> 
> Otherwise we run the risk of having areas whose end is not
> representable, epecially on 32bit.
> 
> 
> Eric
> 
> 
> > Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
> > ---
> >  kernel/kexec_file.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index f9a419cd22d4..26be070d3bdd 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -435,13 +435,12 @@ static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
> >  		if (temp_start < start || temp_start < kbuf->buf_min)
> >  			return 0;
> >  
> > -		temp_end = temp_start + kbuf->memsz - 1;
> > -
> >  		/*
> >  		 * Make sure this does not conflict with any of existing
> >  		 * segments
> >  		 */
> > -		if (kimage_is_destination_range(image, temp_start, temp_end)) {
> > +		if (kimage_is_destination_range(image, temp_start,
> > +						temp_start + kbuf->memsz)) {
> >  			temp_start = temp_start - PAGE_SIZE;
> >  			continue;
> >  		}
> > @@ -475,7 +474,7 @@ static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
> >  		 * Make sure this does not conflict with any of existing
> >  		 * segments
> >  		 */
> > -		if (kimage_is_destination_range(image, temp_start, temp_end)) {
> > +		if (kimage_is_destination_range(image, temp_start, temp_end + 1)) {
> >  			temp_start = temp_start + PAGE_SIZE;
> >  			continue;
> >  		}
> 
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> 

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