[PATCH] /proc/kcore: Update physical address for kcore ram and text

[PATCH] /proc/kcore: Update physical address for kcore ram and text

[Pratyush Anand]

Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
not true and could be misleading, since 0 is a valid physical address.

User space tools like makedumpfile needs to know physical address for
PT_LOAD segments of direct mapped regions. Therefore this patch updates
paddr for such regions. It also sets an invalid paddr (-1) for other
regions, so that user space tool can know whether a physical address
provided in PT_LOAD is correct or not.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 fs/proc/kcore.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 0b80ad87b4d6..ea9f3d1ae830 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
 		phdr->p_flags	= PF_R|PF_W|PF_X;
 		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
 		phdr->p_vaddr	= (size_t)m->addr;
-		phdr->p_paddr	= 0;
+		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
+			phdr->p_paddr	= __pa(m->addr);
+		else
+			phdr->p_paddr	= (elf_addr_t)-1;
 		phdr->p_filesz	= phdr->p_memsz	= m->size;
 		phdr->p_align	= PAGE_SIZE;
 	}
-- 
2.9.3

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Dave Young]

Hi Pratyush
On 01/25/17 at 10:14am, Pratyush Anand wrote:
> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
> not true and could be misleading, since 0 is a valid physical address.

I do not know the history of /proc/kcore, so a question is why the
p_addr was set as 0, if there were some reasons and if this could cause
some risk or breakage.

> 
> User space tools like makedumpfile needs to know physical address for
> PT_LOAD segments of direct mapped regions. Therefore this patch updates
> paddr for such regions. It also sets an invalid paddr (-1) for other
> regions, so that user space tool can know whether a physical address
> provided in PT_LOAD is correct or not.
> 
> Signed-off-by: Pratyush Anand <panand@redhat.com>
> ---
>  fs/proc/kcore.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 0b80ad87b4d6..ea9f3d1ae830 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
>  		phdr->p_flags	= PF_R|PF_W|PF_X;
>  		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
>  		phdr->p_vaddr	= (size_t)m->addr;
> -		phdr->p_paddr	= 0;
> +		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
> +			phdr->p_paddr	= __pa(m->addr);
> +		else
> +			phdr->p_paddr	= (elf_addr_t)-1;
>  		phdr->p_filesz	= phdr->p_memsz	= m->size;
>  		phdr->p_align	= PAGE_SIZE;
>  	}
> -- 
> 2.9.3
> 

Thanks
Dave

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Pratyush Anand]

Hi Dave,

On Wednesday 25 January 2017 11:59 AM, Dave Young wrote:
> Hi Pratyush
> On 01/25/17 at 10:14am, Pratyush Anand wrote:
>> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
>> not true and could be misleading, since 0 is a valid physical address.
> I do not know the history of /proc/kcore, so a question is why the
> p_addr was set as 0, if there were some reasons and if this could cause
> some risk or breakage.
>

I do not know why it was 0, which is a valid physical address. But 
certainly, it might break some user space tools, and those need to be 
fixed. For example, see following code from kexec-tools

kexec/kexec-elf.c:build_mem_phdrs()

435                 if ((phdr->p_paddr + phdr->p_memsz) < phdr->p_paddr) {
436                         /* The memory address wraps */
437                         if (probe_debug) {
438                                 fprintf(stderr, "ELF address wrap 
around\n");
439                         }
440                         return -1;
441                 }

We do not need to perform above check for an invalid physical address.

I think, kexec-tools and makedumpfile will need fixup. I already have 
those fixup which will be sent upstream once this patch makes through.
Pro with this approach is that, it will help to calculate variable like 
page_offset, phys_base from PT_LOAD even when they are randomized and 
therefore will reduce many variable and version specific values in user 
space tools.

~Pratyush

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Kees Cook]

On Mon, Jan 30, 2017 at 11:00 AM, Pratyush Anand <panand@redhat.com> wrote:
> CCing Andrew and Kees for their review comments.
>
>
> On Wednesday 25 January 2017 10:14 AM, Pratyush Anand wrote:
>> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
>> not true and could be misleading, since 0 is a valid physical address.
>>
>> User space tools like makedumpfile needs to know physical address for
>> PT_LOAD segments of direct mapped regions. Therefore this patch updates
>> paddr for such regions. It also sets an invalid paddr (-1) for other
>> regions, so that user space tool can know whether a physical address
>> provided in PT_LOAD is correct or not.
>>
>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>> ---
>> fs/proc/kcore.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
>> index 0b80ad87b4d6..ea9f3d1ae830 100644
>> --- a/fs/proc/kcore.c
>> +++ b/fs/proc/kcore.c
>> @@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int
>> nphdr, int dataoff)
>> phdr->p_flags = PF_R|PF_W|PF_X;
>> phdr->p_offset = kc_vaddr_to_offset(m->addr) + dataoff;
>> phdr->p_vaddr = (size_t)m->addr;
>> - phdr->p_paddr = 0;
>> + if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
>> + phdr->p_paddr = __pa(m->addr);
>> + else
>> + phdr->p_paddr = (elf_addr_t)-1;
>> phdr->p_filesz = phdr->p_memsz = m->size;
>> phdr->p_align = PAGE_SIZE;
>> }
>>

Well, CONFIG_PROC_KCORE is a generalized root KASLR exposure (though
there are lots of such exposures). Why is the actual physical address
needed? Can this just report the virtual address instead? Then the
tool can build a map, but it looks like an identity map, rather than
creating a new physical/virtual memory ASLR offset exposure?

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Pratyush Anand]

On Tuesday 14 February 2017 03:55 AM, Kees Cook wrote:
> On Mon, Jan 30, 2017 at 11:00 AM, Pratyush Anand <panand@redhat.com> wrote:
>> CCing Andrew and Kees for their review comments.
>>
>>
>> On Wednesday 25 January 2017 10:14 AM, Pratyush Anand wrote:
>>> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
>>> not true and could be misleading, since 0 is a valid physical address.
>>>
>>> User space tools like makedumpfile needs to know physical address for
>>> PT_LOAD segments of direct mapped regions. Therefore this patch updates
>>> paddr for such regions. It also sets an invalid paddr (-1) for other
>>> regions, so that user space tool can know whether a physical address
>>> provided in PT_LOAD is correct or not.
>>>
>>> Signed-off-by: Pratyush Anand <panand@redhat.com>
>>> ---
>>> fs/proc/kcore.c | 5 ++++-
>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
>>> index 0b80ad87b4d6..ea9f3d1ae830 100644
>>> --- a/fs/proc/kcore.c
>>> +++ b/fs/proc/kcore.c
>>> @@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int
>>> nphdr, int dataoff)
>>> phdr->p_flags = PF_R|PF_W|PF_X;
>>> phdr->p_offset = kc_vaddr_to_offset(m->addr) + dataoff;
>>> phdr->p_vaddr = (size_t)m->addr;
>>> - phdr->p_paddr = 0;
>>> + if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
>>> + phdr->p_paddr = __pa(m->addr);
>>> + else
>>> + phdr->p_paddr = (elf_addr_t)-1;
>>> phdr->p_filesz = phdr->p_memsz = m->size;
>>> phdr->p_align = PAGE_SIZE;
>>> }
>>>
>
> Well, CONFIG_PROC_KCORE is a generalized root KASLR exposure (though
> there are lots of such exposures). Why is the actual physical address
> needed? Can this just report the virtual address instead? Then the
> tool can build a map, but it looks like an identity map, rather than
> creating a new physical/virtual memory ASLR offset exposure?

Well, having an ASLR offset information can help to translate an 
identity mapped virtual address to a physical address. But that would be 
an additional field in PT_LOAD header structure and an arch dependent value.

Moreover, sending a valid physical address like 0 does not seem right. 
So, IMHO it is better to fix that and send valid physical address when 
available (identity mapped).

Thanks for the review.

~Pratyush

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Pratyush Anand]

Hi Andrew/Kees,

On Tuesday 14 February 2017 07:16 AM, Pratyush Anand wrote:
>>
>> Well, CONFIG_PROC_KCORE is a generalized root KASLR exposure (though
>> there are lots of such exposures). Why is the actual physical address
>> needed? Can this just report the virtual address instead? Then the
>> tool can build a map, but it looks like an identity map, rather than
>> creating a new physical/virtual memory ASLR offset exposure?
>
> Well, having an ASLR offset information can help to translate an
> identity mapped virtual address to a physical address. But that would be
> an additional field in PT_LOAD header structure and an arch dependent
> value.
>
> Moreover, sending a valid physical address like 0 does not seem right.
> So, IMHO it is better to fix that and send valid physical address when
> available (identity mapped).
>
> Thanks for the review.

So, whats the decision on this patch? I see that patch is lying in 
next/master. Should I expect this patch in v4.11-rc1?

Couple of user-space makedumpfile modification will depend on this 
patch. So, we can not get those makedumpfile patches merged until this 
patch hits upstream.

~Pratyush

Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

[Baoquan He]

CC Eric too.

On 02/13/17 at 02:25pm, Kees Cook wrote:
> On Mon, Jan 30, 2017 at 11:00 AM, Pratyush Anand <panand@redhat.com> wrote:
> > CCing Andrew and Kees for their review comments.
> >
> >
> > On Wednesday 25 January 2017 10:14 AM, Pratyush Anand wrote:
> >> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
> >> not true and could be misleading, since 0 is a valid physical address.
> >>
> >> User space tools like makedumpfile needs to know physical address for
> >> PT_LOAD segments of direct mapped regions. Therefore this patch updates
> >> paddr for such regions. It also sets an invalid paddr (-1) for other
> >> regions, so that user space tool can know whether a physical address
> >> provided in PT_LOAD is correct or not.
> >>
> >> Signed-off-by: Pratyush Anand <panand@redhat.com>
> >> ---
> >> fs/proc/kcore.c | 5 ++++-
> >> 1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> >> index 0b80ad87b4d6..ea9f3d1ae830 100644
> >> --- a/fs/proc/kcore.c
> >> +++ b/fs/proc/kcore.c
> >> @@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int
> >> nphdr, int dataoff)
> >> phdr->p_flags = PF_R|PF_W|PF_X;
> >> phdr->p_offset = kc_vaddr_to_offset(m->addr) + dataoff;
> >> phdr->p_vaddr = (size_t)m->addr;
> >> - phdr->p_paddr = 0;
> >> + if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
> >> + phdr->p_paddr = __pa(m->addr);
> >> + else
> >> + phdr->p_paddr = (elf_addr_t)-1;
> >> phdr->p_filesz = phdr->p_memsz = m->size;
> >> phdr->p_align = PAGE_SIZE;
> >> }
> >>
> 
> Well, CONFIG_PROC_KCORE is a generalized root KASLR exposure (though
> there are lots of such exposures). Why is the actual physical address
> needed? Can this just report the virtual address instead? Then the
> tool can build a map, but it looks like an identity map, rather than
> creating a new physical/virtual memory ASLR offset exposure?

HPE asked to add a dumped vmcore size estimate feature to makedumpfile,
just like HP UNIX does. So I added a --mem-usage option to makedumpfile
and use /proc/kcore to analyze the memory of 1st kernel. Since /proc/kcore
is a elf file which contains the mm layout of 1st kernel, it can help us
estimate how much disk space need be reserved. Later s390x people also
add support for this feature.

With kaslr enabled, page_offset becomes uncertain, and in kernel Eric
doesn't suggest exporting them into vmcoreinfo. So Pratyush tried to add
physical address of direct mapping regions. For kaslr, kcore has
exported those randomized starting address, I am not sure if it's risky
to export physical address.

It's close to our rhel dev cycle deadline, we hope this can be merged
soon. I believe we can discuss it and improve it any time if risk is
felt.

Thanks
Baoquan