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A livepatch module can contain a special relocation section
.klp.rela.<objname>.<secname> to apply its relocations at the appropriate
time and to additionally access local and unexported symbols. When
<objname> points to another module, such relocations are processed
separately from the regular module relocation process. For instance, only
when the target <objname> actually becomes loaded.
With CONFIG_STRICT_MODULE_RWX, when the livepatch core decides to apply
these relocations, their processing results in the following bug:
[ 25.827238] BUG: unable to handle page fault for address: 00000000000012ba
[ 25.827819] #PF: supervisor read access in kernel mode
[ 25.828153] #PF: error_code(0x0000) - not-present page
[ 25.828588] PGD 0 P4D 0
[ 25.829063] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 25.829742] CPU: 2 UID: 0 PID: 452 Comm: insmod Tainted: G O K 6.13.0-rc4-00078-g059dd502b263 #7820
[ 25.830417] Tainted: [O]=OOT_MODULE, [K]=LIVEPATCH
[ 25.830768] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-20220807_005459-localhost 04/01/2014
[ 25.831651] RIP: 0010:memcmp+0x24/0x60
[ 25.832190] Code: [...]
[ 25.833378] RSP: 0018:ffffa40b403a3ae8 EFLAGS: 00000246
[ 25.833637] RAX: 0000000000000000 RBX: ffff93bc81d8e700 RCX: ffffffffc0202000
[ 25.834072] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 00000000000012ba
[ 25.834548] RBP: ffffa40b403a3b68 R08: ffffa40b403a3b30 R09: 0000004a00000002
[ 25.835088] R10: ffffffffffffd222 R11: f000000000000000 R12: 0000000000000000
[ 25.835666] R13: ffffffffc02032ba R14: ffffffffc007d1e0 R15: 0000000000000004
[ 25.836139] FS: 00007fecef8c3080(0000) GS:ffff93bc8f900000(0000) knlGS:0000000000000000
[ 25.836519] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 25.836977] CR2: 00000000000012ba CR3: 0000000002f24000 CR4: 00000000000006f0
[ 25.837442] Call Trace:
[ 25.838297] <TASK>
[ 25.841083] __write_relocate_add.constprop.0+0xc7/0x2b0
[ 25.841701] apply_relocate_add+0x75/0xa0
[ 25.841973] klp_write_section_relocs+0x10e/0x140
[ 25.842304] klp_write_object_relocs+0x70/0xa0
[ 25.842682] klp_init_object_loaded+0x21/0xf0
[ 25.842972] klp_enable_patch+0x43d/0x900
[ 25.843572] do_one_initcall+0x4c/0x220
[ 25.844186] do_init_module+0x6a/0x260
[ 25.844423] init_module_from_file+0x9c/0xe0
[ 25.844702] idempotent_init_module+0x172/0x270
[ 25.845008] __x64_sys_finit_module+0x69/0xc0
[ 25.845253] do_syscall_64+0x9e/0x1a0
[ 25.845498] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 25.846056] RIP: 0033:0x7fecef9eb25d
[ 25.846444] Code: [...]
[ 25.847563] RSP: 002b:00007ffd0c5d6de8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 25.848082] RAX: ffffffffffffffda RBX: 000055b03f05e470 RCX: 00007fecef9eb25d
[ 25.848456] RDX: 0000000000000000 RSI: 000055b001e74e52 RDI: 0000000000000003
[ 25.848969] RBP: 00007ffd0c5d6ea0 R08: 0000000000000040 R09: 0000000000004100
[ 25.849411] R10: 00007fecefac7b20 R11: 0000000000000246 R12: 000055b001e74e52
[ 25.849905] R13: 0000000000000000 R14: 000055b03f05e440 R15: 0000000000000000
[ 25.850336] </TASK>
[ 25.850553] Modules linked in: deku(OK+) uinput
[ 25.851408] CR2: 00000000000012ba
[ 25.852085] ---[ end trace 0000000000000000 ]---
The problem is that the .klp.rela.<objname>.<secname> relocations are
processed after the module was already formed and mod->rw_copy was reset.
However, the code in __write_relocate_add() calls
module_writable_address() which translates the target address 'loc' still
to 'loc + (mem->rw_copy - mem->base)', with mem->rw_copy now being 0.
Fix the problem by returning directly 'loc' in module_writable_address()
when the module is already formed. Function __write_relocate_add() knows
to use text_poke() in such a case.
Link: https://lkml.kernel.org/r/20250107153507.14733-1-petr.pavlu@suse.com
Fixes: 0c133b1e78 ("module: prepare to handle ROX allocations for text")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reported-by: Marek Maslanka <mmaslanka@google.com>
Closes: https://lore.kernel.org/linux-modules/CAGcaFA2hdThQV6mjD_1_U+GNHThv84+MQvMWLgEuX+LVbAyDxg@mail.gmail.com/
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.