2018-07-05 14:56:50

by Oscar Salvador

Subject: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

From: Oscar Salvador <[email protected]>

The current code does not make sure to page align bss before calling
vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
due to the requested lenght not being correctly aligned.

Let us make sure to align it properly.

Signed-off-by: Oscar Salvador <[email protected]>
Tested-by: Tetsuo Handa <[email protected]>
Reported-by: [email protected]
---
fs/binfmt_elf.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 0ac456b52bdd..816cc921cf36 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
goto out_free_ph;
}

- len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
- ELF_MIN_ALIGN - 1);
- bss = eppnt->p_memsz + eppnt->p_vaddr;
+ len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
+ bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
if (bss > len) {
error = vm_brk(len, bss - len);
if (error)
--
2.13.6

2018-07-05 15:46:25

by Kees Cook

Subject: Re: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

On Thu, Jul 5, 2018 at 7:55 AM, <[email protected]> wrote:
> From: Oscar Salvador <[email protected]>
>
> The current code does not make sure to page align bss before calling
> vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
> due to the requested lenght not being correctly aligned.
>
> Let us make sure to align it properly.
>
> Signed-off-by: Oscar Salvador <[email protected]>
> Tested-by: Tetsuo Handa <[email protected]>
> Reported-by: [email protected]

Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
only, and libc5 and earlier only.

Regardless, this appears to match the current bss alignment logic in
the main elf loader, so:

Acked-by: Kees Cook <[email protected]>

-Kees

> ---
> fs/binfmt_elf.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 0ac456b52bdd..816cc921cf36 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
> goto out_free_ph;
> }
>
> - len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
> - ELF_MIN_ALIGN - 1);
> - bss = eppnt->p_memsz + eppnt->p_vaddr;
> + len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
> + bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
> if (bss > len) {
> error = vm_brk(len, bss - len);
> if (error)
> --
> 2.13.6
>



--
Kees Cook
Pixel Security

2018-07-06 07:16:02

by Oscar Salvador

Subject: Re: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

On Thu, Jul 05, 2018 at 08:44:18AM -0700, Kees Cook wrote:
> On Thu, Jul 5, 2018 at 7:55 AM, <[email protected]> wrote:
> > From: Oscar Salvador <[email protected]>
> >
> > The current code does not make sure to page align bss before calling
> > vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
> > due to the requested lenght not being correctly aligned.
> >
> > Let us make sure to align it properly.
> >
> > Signed-off-by: Oscar Salvador <[email protected]>
> > Tested-by: Tetsuo Handa <[email protected]>
> > Reported-by: [email protected]
>
> Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
> only, and libc5 and earlier only.
>
> Regardless, this appears to match the current bss alignment logic in
> the main elf loader, so:
>
> Acked-by: Kees Cook <[email protected]>
>
> -Kees
>
> > ---
> > fs/binfmt_elf.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index 0ac456b52bdd..816cc921cf36 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
> > goto out_free_ph;
> > }
> >
> > - len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
> > - ELF_MIN_ALIGN - 1);
> > - bss = eppnt->p_memsz + eppnt->p_vaddr;
> > + len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
> > + bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
> > if (bss > len) {
> > error = vm_brk(len, bss - len);
> > if (error)
> > --
> > 2.13.6
> >
CC Andrew

Hi Andrew,

in case this patch gets accepted, does it have to go through your tree?
Or is it for someone else to take it?

Thanks
--
Oscar Salvador
SUSE L3

2018-07-06 19:25:54

by Kees Cook

Subject: Re: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

On Fri, Jul 6, 2018 at 12:13 AM, Oscar Salvador
<[email protected]> wrote:
> On Thu, Jul 05, 2018 at 08:44:18AM -0700, Kees Cook wrote:
>> On Thu, Jul 5, 2018 at 7:55 AM, <[email protected]> wrote:
>> > From: Oscar Salvador <[email protected]>
>> >
>> > The current code does not make sure to page align bss before calling
>> > vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
>> > due to the requested lenght not being correctly aligned.
>> >
>> > Let us make sure to align it properly.
>> >
>> > Signed-off-by: Oscar Salvador <[email protected]>
>> > Tested-by: Tetsuo Handa <[email protected]>
>> > Reported-by: [email protected]
>>
>> Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
>> only, and libc5 and earlier only.
>>
>> Regardless, this appears to match the current bss alignment logic in
>> the main elf loader, so:
>>
>> Acked-by: Kees Cook <[email protected]>
>>
>> -Kees
>>
>> > ---
>> > fs/binfmt_elf.c | 5 ++---
>> > 1 file changed, 2 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
>> > index 0ac456b52bdd..816cc921cf36 100644
>> > --- a/fs/binfmt_elf.c
>> > +++ b/fs/binfmt_elf.c
>> > @@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
>> > goto out_free_ph;
>> > }
>> >
>> > - len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
>> > - ELF_MIN_ALIGN - 1);
>> > - bss = eppnt->p_memsz + eppnt->p_vaddr;
>> > + len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
>> > + bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
>> > if (bss > len) {
>> > error = vm_brk(len, bss - len);
>> > if (error)
>> > --
>> > 2.13.6
>> >
> CC Andrew
>
> Hi Andrew,
>
> in case this patch gets accepted, does it have to go through your tree?
> Or is it for someone else to take it?

(FWIW, binfmt_elf changes have traditionally gone through -mm, yes.)

-Kees

--
Kees Cook
Pixel Security

2018-07-06 22:56:23

by Andrew Morton

Subject: Re: [PATCH] fs, elf: Make sure to page align bss in load_elf_library

On Thu, 5 Jul 2018 08:44:18 -0700 Kees Cook <[email protected]> wrote:

> On Thu, Jul 5, 2018 at 7:55 AM, <[email protected]> wrote:
> > From: Oscar Salvador <[email protected]>
> >
> > The current code does not make sure to page align bss before calling
> > vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
> > due to the requested lenght not being correctly aligned.
> >
> > Let us make sure to align it properly.
> >
> > Signed-off-by: Oscar Salvador <[email protected]>
> > Tested-by: Tetsuo Handa <[email protected]>
> > Reported-by: [email protected]
>
> Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
> only, and libc5 and earlier only.

Presumably doesn't happen much, but people who *are* enabling this will
want the fix, so I added the cc:stable.