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Dmitry Safonov authored
Commit: 90954e7b ("x86/coredump: Use pr_reg size, rather that TIF_IA32 flag") changed the coredumping code to construct the elf coredump file 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: 32-victim[19266]: segfault at f775ef65 ip 00000000f775ef65 sp 00000000f776aa50 error 14 BUG: unable to handle kernel paging request at ffffffffffffffff IP: [<ffffffff81332ce0>] strlen+0x0/0x20 [...] Call Trace: [] elf_core_dump+0x11a9/0x1480 [] do_coredump+0xa6b/0xe60 [] get_signal+0x1a8/0x5c0 [] do_signal+0x23/0x660 [] exit_to_usermode_loop+0x34/0x65 [] prepare_exit_to_usermode+0x2f/0x40 [] retint_user+0x8/0x10 That's because we have 64-bit registers set (with according total size) and we're writing it to elf_thread_core_info which has smaller size on !CONFIG_X86_X32_ABI. That lead to overwriting ELF notes part. Tested on 32-, 64-bit ELF crashes and on 32-bit binaries that have jumped with 64-bit code selector - all is readable with gdb. Signed-off-by:
Dmitry Safonov <dsafonov@virtuozzo.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-mm@kvack.org Fixes: 90954e7b ("x86/coredump: Use pr_reg size, rather that TIF_IA32 flag") Signed-off-by:
Ingo Molnar <mingo@kernel.org>
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