Re: [LTP] [PATCH v8 2/2] coredump02: Verify ELF structure and notes

[Andrea Cervesato via ltp <ltp@lists.linux.it>]

Hi Cyril,

> I would have expected that the elf headers are aligned properly and
> since we loaded the whole file into aligned buffer (malloc() aligns
> properly), it should be safe to just cast the desc pointer into the
> strcut elf_prpsinfo *info = desc;  and acces info.pr_name directly from
> the buffer.

I made an analysis and I found out this is not valid.

It seems like we can't use the cast in x86_64 because it requires a
8 bytes aligned struct.

The kernel writes:

12 bytes: note header
 5 bytes: "CORE" and its ending zero
 3 bytes: padding
---
20 bytes total

Although malloc() aligns the buffer’s starting address, the descriptor
inside it is not 8-byte aligned. For example:

Buffer starts at address:    4096
Notes start at file offset:  624  (64 + 10 × 56)
First descriptor is another: 20 bytes later
Descriptor's memory address: 4740

So memory is not 8 bytes aligned and when we cast to a pointer we
might be misaligned when accessing pr_pid.

We still need memcpy(), so we make sure we are accessing the right
portion of the memory.

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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