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

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Date:   Mon, 13 Feb 2017 14:25:01 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Pratyush Anand <panand@...hat.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Dave Anderson <anderson@...hat.com>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

On Mon, Jan 30, 2017 at 11:00 AM, Pratyush Anand <panand@...hat.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@...hat.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