In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mips: select CONFIG_WEAK_REORDERING_BEYOND_LLSC from CONFIG_EYEQ<\/p>\n
On I6500 CPU cores, lld and scd give no ordering guarantees (same as all
\nother instructions). To respect the assumption that arch_cmpxchg() is
\nfully ordered, we must inject sync instructions above and below our
\nlld\/scd loops using the already in place WEAK_REORDERING_BEYOND_LLSC
\ninfrastructure.<\/p>\n
Otherwise, bad things can happen:<\/p>\n
[ 34.054496] CPU 3 Unable to handle kernel paging request at virtual address 0000000000000000, epc == a80000080838e01c, ra == a80000080838dfc4
\n[ 34.054559] Oops[#1]:
\n[ 34.069561] CPU: 3 UID: 0 PID: 170 Comm: pipe_race Not tainted 7.2.0-rc6-01553-gb73c35220968-dirty #103 VOLUNTARY
\n[ 34.079932] Hardware name: Mobile EyeQ5 MP5 Evaluation board
\n[ 34.085592] $ 0 : 0000000000000000 0000000000000001 0000000000000000 0000000000000000
\n[ 34.093616] $ 4 : a800000808ee2618 000000000b7a879d 0000000000001000 0000000000000000
\n[ 34.101638] $ 8 : 0000000000e3f2c9 0000000000000000 a800000808a2a9f8 0000000000000000
\n[ 34.109660] $12 : a8000008139ffcd8 ffffffff84080018 a80000080837fae0 7878787878787878
\n[ 34.117682] $16 : a800000807e82940 0000000000001000 0000000000000000 0000000000000000
\n[ 34.125704] $20 : a800000802920e00 a8000008139ffdf8 a800000802649400 0000000000e3f2c9
\n[ 34.133726] $24 : 0000000000000006 00000001200406e0
\n[ 34.141783] $28 : a8000008139fc000 a8000008139ffd10 0000000000e3f2c8 a80000080838dfc4
\n[ 34.149837] epc : a80000080838e01c anon_pipe_read+0xd4\/0x428
\n[ 34.155697] ra : a80000080838dfc4 anon_pipe_read+0x7c\/0x428
\n[ 34.161549] Status: 140000e3 KX SX UX KERNEL EXL IE
\n[ 34.166551] Cause : 40800408 (ExcCode 02)
\n[ 34.170574] BadVA : 0000000000000000
\n[ 34.174161] PrId : 0001b028 (MIPS I6500)
\n[ 34.178183] Process pipe_race (pid: 170, threadinfo=000000005ca35720, task=00000000e1013890, tls=000000014ebbb780)
\n[ 34.188568] Stack : a800000802649400 0000000000000000 0000000000000000 a8000008139ffdd0
\n[ 34.196623]\t 0000000000000fba a800000808ee0000 0000000000000001 a8000008130c3e80
\n[ 34.204676]\t a8000008080d1280 a8000008139ffd58 a8000008139ffd58 1dbd2b22ea1dd500
\n[ 34.212729]\t a800000802649400 a800000808ee0000 ffffffffffffffea 0000000000000001
\n[ 34.220783]\t 0000000000001000 0000000000000000 00000001200ae518 ffffffffffffffff
\n[ 34.228836]\t 000000fffbe0e530 a80000080837edf4 000000fffbe0e530 0000000000000000
\n[ 34.236890]\t 0000000000000000 0000000000000000 000000014ebb55a0 0000000000001000
\n[ 34.244943]\t 0000000000000001 a800000802649400 0000000000000000 0000000000000000
\n[ 34.252996]\t 0000000000000000 0000400400000000 0000000000000000 1dbd2b22ea1dd500
\n[ 34.261049]\t 00000000140000e3 a800000802649400 a800000802649400 a800000808ee0000
\n[ 34.269103]\t …
\n[ 34.271568] Call Trace:
\n[ 34.274026] [] anon_pipe_read+0xd4\/0x428
\n[ 34.279533] [] vfs_read+0x25c\/0x318
\n[ 34.284607] [] ksys_read+0x104\/0x138
\n[ 34.289763] [] syscall_common+0x44\/0x68
\n[ 34.295187]
\n[ 34.296689] Code: f84000cf 02209825 de020010 d8400004 02002825 0040f809 02802025 f84000c3
\n[ 34.306504]
\n[ 34.308099] —[ end trace 0000000000000000 ]—<\/p>\n
My initial reproducer was the xdp-tools test suite. A standalone
\nreproducer would be an lld\/scd loop that, when the read is reordered by
\nthe CPU, triggers a fault. We can achieve this from userspace by
\nstressing an anonymous pipe, which uses a mutex. Program used:<\/p>\n
\t\/\/ SPDX-License-Identifier: GPL-2.0
\n\t\/\/ pipe_race.c – reproducer for MIPS LL\/SC reordering vs fs\/pipe.c
\n\t\/\/
\n\t\/\/ Two userspace processes on an anonymous pipe:
\n\t\/\/ parent = writer: tight write() loop
\n\t\/\/ child = reader: tight read() loop<\/p>\n
\t#define _GNU_SOURCE
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n\t#include
\n—truncated—<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mips: select CONFIG_WEAK_REORDERING_BEYOND_LLSC from CONFIG_EYEQ<\/p>\n
On I6500 CPU cores, lld and scd give no ordering guarantees (same<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-33297","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/33297","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=33297"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=33297"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=33297"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}