From: "Maciej W. Rozycki" <macro@orcam.me.uk>
To: Alan Modra <amodra@gmail.com>
Cc: binutils@sourceware.org, Chenghua Xu <paul.hua.gm@gmail.com>
Subject: Re: Protect mips_hi16_list from fuzzed debug info
Date: Tue, 7 Feb 2023 14:11:23 +0000 (GMT) [thread overview]
Message-ID: <alpine.DEB.2.21.2302071347490.11790@angie.orcam.me.uk> (raw)
In-Reply-To: <Y+DzhUGfFBaLPJiD@squeak.grove.modra.org>
On Mon, 6 Feb 2023, Alan Modra wrote:
> This is another fix for the testcase mentioned in
> https://sourceware.org/pipermail/binutils/2023-February/125915.html
> either of which will stop the addr2line segfault. This one also fixes
> a potential problem when linking corrupted debug info.
Hmm, from the other message I gather DWARF info is not going to be
processed twice anymore, so why is this change to the MIPS backend also
required?
Also would it be possible to have a MIPS test case for your change?
Orchestrating HI16/LO16 relocations in a debug section should be pretty
straightforward with the use of the `.reloc' pseudo-op. This might help
me understand what is really going on here.
Also one concern about code proposed itself, see below.
> @@ -2596,38 +2600,41 @@ _bfd_mips_elf_lo16_reloc (bfd *abfd, arelent *reloc_entry, asymbol *symbol,
[...]
> + if (!tdata->freeze_mips_hi16_list)
This conditional ought to wrap all the preceding code in the function as
well (including the declaration block), because it's sole purpose is to
retrieve `vallo', which is only used within the `while' loop now placed
under the conditional...
> + while (tdata->mips_hi16_list != NULL)
> + {
> + bfd_reloc_status_type ret;
> + struct mips_hi16 *hi;
> +
> + hi = tdata->mips_hi16_list;
> +
> + /* R_MIPS*_GOT16 relocations are something of a special case.
> + We want to install the addend in the same way as for a
> + R_MIPS*_HI16 relocation (with a rightshift of 16).
> + However, since GOT16 relocations can also be used with
> + global symbols, their howto has a rightshift of 0. */
> + if (hi->rel.howto->type == R_MIPS_GOT16)
> + hi->rel.howto = MIPS_ELF_RTYPE_TO_HOWTO (abfd, R_MIPS_HI16, false);
> + else if (hi->rel.howto->type == R_MIPS16_GOT16)
> + hi->rel.howto = MIPS_ELF_RTYPE_TO_HOWTO (abfd, R_MIPS16_HI16, false);
> + else if (hi->rel.howto->type == R_MICROMIPS_GOT16)
> + hi->rel.howto = MIPS_ELF_RTYPE_TO_HOWTO (abfd, R_MICROMIPS_HI16,
> + false);
> +
> + /* VALLO is a signed 16-bit number. Bias it by 0x8000 so that
> + any carry or borrow will induce a change of +1 or -1 in the
> + high part. */
> + hi->rel.addend += (vallo + 0x8000) & 0xffff;
... here.
> + /* Debug info should not contain hi16 or lo16 relocs. If it does
> + then someone is playing fuzzing games. Altering the hi16 list
> + during linking when printing an error message is bad. */
And I really cannot extract the meaning of the second sentence here. I
mean I know what it literally means, but that does not really tell me
anything. Why would altering the list be a problem given that we're
bailing out anyway? I'm confused.
Maciej
next prev parent reply other threads:[~2023-02-07 14:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-06 12:33 Alan Modra
2023-02-07 14:11 ` Maciej W. Rozycki [this message]
2023-02-08 0:32 ` Alan Modra
2023-02-08 23:28 ` Maciej W. Rozycki
2023-02-09 0:29 ` Alan Modra
2023-02-09 1:26 ` Maciej W. Rozycki
2023-02-09 10:14 ` Alan Modra
2023-02-10 18:13 ` Maciej W. Rozycki
2023-05-20 11:41 ` Alan Modra
2023-05-20 11:44 ` coff-mips refhi list Alan Modra
2023-05-23 21:19 ` Protect mips_hi16_list from fuzzed debug info Maciej W. Rozycki
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