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Bug #14427

closed

amd64 kobj_reloc can infinite loop on bad reloc type

Added by Robert Mustacchi 7 months ago. Updated 7 months ago.

Status:
Closed
Priority:
Normal
Category:
kernel
Start date:
Due date:
% Done:

100%

Estimated time:
Difficulty:
Medium
Tags:
Gerrit CR:

Description

While doing development on a system, I had screwed things up and found myself in an infinite loop in krtld. The start of the message was:

module /kernel/misc/amd64/kmdbmod: text at [0xfffffffffc1f8000, 0xfffffffffc2c73a7] data at 0xfffffffffc2c73c0
module /kernel/misc/amd64/ctf: text at [0xfffffffffbd8f2e0, 0xfffffffffbd9a7d7] data at 0xfffffffffc300900
krtld: invalid relocation type 6304771 at 0x602403: file=/kernel/misc/amd64/kmdbmod
...

After that point, we'd continue to loop with invalid relocations. While there was certainly a problem with the input data in this case, we shouldn't have been in an infinite loop. If we dig into the ammd64 do_relocate, here are the relevant facts:

  • We are processing through the while (reladdr < rend) { loop here.
  • At the start of the loop, the first thing that we do is increment the symnum variable; however, that has no bearing on the actual relocation address
  • The relocation address is initially set before the loop and then critically adjusted after we check for the relocation type.
  • When we have an invalid relocation type, note an error; however, we continue processing by restarting the loop, but this means that we never change the actual reladdr, leading us to always look at the same data

In this case, I believe we should just error out immediately like we do in the case of bad string table index. While normally we try to find all missing symbols so it's not a game of whackamole, in this case it probably is representative that we have bad data as opposed to merely a missing dependency (the usual reason do_relocate fails).

With this in place, the errant module in question ends up providing the following output:

module /kernel/misc/amd64/kmdbmod: text at [0xfffffffffc1f8000, 0xfffffffffc2c73a7] data at 0xfffffffffc2c73c0
module /kernel/misc/amd64/ctf: text at [0xfffffffffbd8f2e0, 0xfffffffffbd9a7d7] data at 0xfffffffffc300900
krtld: invalid relocation type 6304771 at 0x602403: file=/kernel/misc/amd64/kmdbmod
do_relocations: /kernel/misc/amd64/kmdbmod do_relocate failed
krtld: error during initial load/link phase
Actions #1

Updated by Electric Monk 7 months ago

  • Gerrit CR set to 1969
Actions #2

Updated by Robert Mustacchi 7 months ago

In addition to the broken systems, I also just tested this on normal bits that work and verified we still boot.

Actions #3

Updated by Robert Mustacchi 7 months ago

  • Description updated (diff)
Actions #4

Updated by Electric Monk 7 months ago

  • Status changed from New to Closed
  • % Done changed from 0 to 100

git commit 6d25b15cb097cca4822fec6dcaf12fcd345b1a2a

commit  6d25b15cb097cca4822fec6dcaf12fcd345b1a2a
Author: Robert Mustacchi <rm@fingolfin.org>
Date:   2022-01-22T19:57:48.000Z

    14427 amd64 kobj_reloc can infinite loop on bad reloc type
    Reviewed by: Andy Fiddaman <andy@omnios.org>
    Reviewed by: Toomas Soome <tsoome@me.com>
    Approved by: Rich Lowe <richlowe@richlowe.net>

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