linux-kernel - Re: [PATCH v6 09/13] module: Move kallsyms support into a separate file

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Message-ID: <0ea89614-9bab-99f5-47a8-2a2996c38966@csgroup.eu>
Date:   Mon, 21 Feb 2022 09:35:06 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Aaron Tomlin <atomlin@...hat.com>, mcgrof@...nel.org
Cc:     cl@...ux.com, pmladek@...e.com, mbenes@...e.cz,
        akpm@...ux-foundation.org, jeyu@...nel.org,
        linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        live-patching@...r.kernel.org, atomlin@...mlin.com,
        ghalat@...hat.com, allen.lkml@...il.com, joe@...ches.com,
        msuchanek@...e.de, oleksandr@...alenko.name
Subject: Re: [PATCH v6 09/13] module: Move kallsyms support into a separate
 file



Le 21/02/2022 à 09:15, Christophe Leroy a écrit :
> 
> 
> Le 18/02/2022 à 22:25, Aaron Tomlin a écrit :
>> No functional change.
>>
>> This patch migrates kallsyms code out of core module
>> code kernel/module/kallsyms.c
>>
>> Signed-off-by: Aaron Tomlin <atomlin@...hat.com>
> 
> With this patch I get an Oops:
> 
> [   36.421711] BUG: Unable to handle kernel data access on write at 
> 0xbe79bb40
> [   36.428435] Faulting instruction address: 0xc008b74c
> [   36.433342] Oops: Kernel access of bad area, sig: 11 [#1]
> [   36.438672] BE PAGE_SIZE=16K PREEMPT CMPC885
> [   36.442947] SAF3000 DIE NOTIFICATION
> [   36.446421] Modules linked in:
> [   36.449436] CPU: 0 PID: 374 Comm: insmod Not tainted 
> 5.17.0-rc4-s3k-dev-02274-g7d4ec8831803 #1016
> [   36.458211] NIP:  c008b74c LR: c00897ac CTR: c001145c
> [   36.463200] REGS: caf8bcf0 TRAP: 0300   Not tainted 
> (5.17.0-rc4-s3k-dev-02274-g7d4ec8831803)
> [   36.471633] MSR:  00009032 <EE,ME,IR,DR,RI>  CR: 24002842  XER: 00000000
> [   36.478261] DAR: be79bb40 DSISR: c2000000
> [   36.478261] GPR00: c00899a0 caf8bdb0 c230a980 be74c000 caf8beb8 
> 00000008 00000000 c035629c
> [   36.478261] GPR08: be75c000 caf9c9fc be79bb40 00000004 24002842 
> 100d166a 00000290 00000000
> [   36.478261] GPR16: c0747320 caf9c9fc c11ff918 caf9b2a7 be75c290 
> 00000550 00000022 c0747210
> [   36.478261] GPR24: c11ff8e8 be74c000 c11ff8fc 100b8820 00000000 
> 00000000 be74c000 caf8beb8
> [   36.516729] NIP [c008b74c] add_kallsyms+0x48/0x30c
> [   36.521465] LR [c00897ac] load_module+0x16f8/0x2504

Fixup:

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 6c8f1f390cf5..2ee8d2e67068 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -171,8 +171,7 @@ void add_kallsyms(struct module *mod, const struct 
load_info *info)
  	Elf_Shdr *symsec = &info->sechdrs[info->index.sym];

  	/* Set up to point into init section. */
-	mod->kallsyms = (struct mod_kallsyms __rcu *)mod->init_layout.base +
-		info->mod_kallsyms_init_off;
+	mod->kallsyms = (void __rcu *)mod->init_layout.base + 
info->mod_kallsyms_init_off;

  	/* The following is safe since this pointer cannot change */
  	rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr;


Christophe