Hi, Kazu
Thank you for the fix.
On Thu, Dec 5, 2024 at 5:10 PM <devel-request@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Date: Thu, 5 Dec 2024 01:30:34 +0000
From: HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx>
Subject: [PATCH] Fix infinite loop during module
symbols initialization
To: "devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx"
<devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Message-ID: <1733362232-30303-1-git-send-email-k-hagio-ab@xxxxxxx>
Content-Type: text/plain; charset="iso-2022-jp"
From: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
An infinite loop occured in mod_symname_hash_install() during module
symbols initialization on 6.13-rc1 kernel.
Not sure which kernel patch caused this (probably execmem patches), a
gap region between a module text and another module's one has gone, i.e.
they became consecutive. In this case, as we set a module's pseudo end
symbol to "base + size" value, it's equal to another module's pseudo
start symbol. This and qsort() for st->ext_module_symbtable cause
region overlaps like this:
sp sp->value sp->name
823ac68 ffffffffc0800000 _MODULE_TEXT_START_dm_mod
...
8242080 ffffffffc0814ad0 __pfx_dm_devt_from_path
82420a8 ffffffffc0814ae0 dm_devt_from_path
82420d0 ffffffffc0815000 _MODULE_TEXT_START_libcrc32c << same value
82420f8 ffffffffc0815000 __pfx_crc32c << and
8242120 ffffffffc0815000 _MODULE_TEXT_END_dm_mod << overlap
Strange, this looks like a kernel module issue?
8242148 ffffffffc0815010 crc32c
8242170 ffffffffc0815080 __pfx_libcrc32c_mod_fini
...
8242238 ffffffffc0816000 _MODULE_TEXT_END_libcrc32c
As a result, mod_symtable_hash_install_range() can add a module symbol
two times, which makes a self-loop. This causes an infinite loop in
mod_symname_hash_install().
Core was generated by `crash'.
#0 mod_symname_hash_install (spn=0x75e6bc0) at symbols.c:1236
1236 if (!sp->name_hash_next ||
(gdb) p sp
$1 = (struct syment *) 0x75e6670
(gdb) p sp->name
$2 = 0x7c03573 "_MODULE_TEXT_START_libcrc32c"
(gdb) p sp->name_hash_next
$3 = (struct syment *) 0x75e6670 << self-loop
To avoid this, fix module pseudo end symbols to "base + size - 1".
So far I haven't thought of a better solution yet. For the patch: Ack.
Thanks
Lianbo
Signed-off-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
---
symbols.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/symbols.c b/symbols.c
index a26bdc1a3461..0fe5d2951c7e 100644
--- a/symbols.c
+++ b/symbols.c
@@ -2196,7 +2196,7 @@ store_module_symbols_6_4(ulong total, int mods_installed)
if (!lm->mem[t].size)
continue;
- st->ext_module_symtable[mcnt].value = lm->mem[t].base + lm->mem[t].size;
+ st->ext_module_symtable[mcnt].value = lm->mem[t].base + lm->mem[t].size - 1;
st->ext_module_symtable[mcnt].type = 'm';
st->ext_module_symtable[mcnt].flags |= MODULE_SYMBOL;
sprintf(buf2, "%s%s", module_tag[t].end, mod_name);
--
2.31.1
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