Re: [PATCH] x86/coredump: always use user_regs_struct for compat_elf_gregset_t

From: Andy Lutomirski
Date: Thu Dec 08 2016 - 18:15:19 EST

On Nov 23, 2016 10:16 AM, "Dmitry Safonov" <dsafonov@xxxxxxxxxxxxx> wrote:
> From commit 90954e7b9407 ("x86/coredump: Use pr_reg size, rather that
> TIF_IA32 flag") elf coredump file is constructed according to register
> set size - and that's good: if binary crashes with 32-bit code selector,
> generate 32-bit ELF core, otherwise - 64-bit core.
> That was made for restoring 32-bit applications on x86_64: we want
> 32-bit application after restore to generate 32-bit ELF dump on crash.
> All was quite good and recently I started reworking 32-bit applications
> dumping part of CRIU: now it has two parasites (32 and 64) for seizing
> compat/native tasks, after rework it'll have one parasite, working in
> 64-bit mode, to which 32-bit prologue long-jumps during infection.
> And while it has worked for my work machine, in VM with
> !CONFIG_X86_X32_ABI during reworking I faced that segfault in 32-bit
> binary, that has long-jumped to 64-bit mode results in dereference
> of garbage:

Can you point to the actual line that's crashing? I'm wondering if we
have code that should be made more robust.