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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b49cb8b4b98sm8384889a12.19.2025.08.26.00.20.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Aug 2025 00:20:48 -0700 (PDT) Message-ID: <80d7313a-0f0c-494d-b2ad-2662d1992b2b@suse.com> Date: Tue, 26 Aug 2025 09:20:41 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] module: pr_debug when there is no version info From: Petr Pavlu To: Wang Jinchao Cc: Luis Chamberlain , Daniel Gomez , Sami Tolvanen , linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org References: <20250721045224.391745-1-wangjinchao600@gmail.com> <3992b57d-3d8b-4d60-bc4a-f227f712dcca@suse.com> <86062810-ff6b-4181-83b7-dfe443ff4012@gmail.com> <9b768f91-121a-4072-88b2-36cb48be3917@suse.com> Content-Language: en-US In-Reply-To: <9b768f91-121a-4072-88b2-36cb48be3917@suse.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/22/25 10:25 AM, Petr Pavlu wrote: > On 7/22/25 5:08 AM, Wang Jinchao wrote: >> On 7/21/25 22:40, Petr Pavlu wrote: >>> On 7/21/25 6:52 AM, Wang Jinchao wrote: >>>> When there is no version information, modprobe and insmod only >>>> report "invalid format". >>>> Print the actual cause to make it easier to diagnose the issue. >>>> This helps developers quickly identify version-related module >>>> loading failures. >>>> Signed-off-by: Wang Jinchao >>>> --- >>>> kernel/module/version.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/kernel/module/version.c b/kernel/module/version.c >>>> index 2beefeba82d9..bc28c697ff3a 100644 >>>> --- a/kernel/module/version.c >>>> +++ b/kernel/module/version.c >>>> @@ -42,8 +42,10 @@ int check_version(const struct load_info *info, >>>> } >>>> /* No versions at all? modprobe --force does this. */ >>>> - if (versindex == 0) >>>> + if (versindex == 0) { >>>> + pr_debug("No version info for module %s\n", info->name); >>>> return try_to_force_load(mod, symname) == 0; >>>> + } >>>> versions = (void *)sechdrs[versindex].sh_addr; >>>> num_versions = sechdrs[versindex].sh_size >>> >>> I think it would be better to instead improve the behavior of >>> try_to_force_load(). The function should print the error reason prior to >>> returning -ENOEXEC. This would also help its two other callers, >>> check_modinfo() and check_export_symbol_versions(). >>> >>> Additionally, I suggest moving the check to ensure version information >>> is available for imported symbols earlier in the loading process. >>> A suitable place might be check_modstruct_version(). This way the check >>> is performed only once per module. >>> >>> The following is a prototype patch: >>> >>> diff --git a/kernel/module/main.c b/kernel/module/main.c >>> index c2c08007029d..c1ccd343e8c3 100644 >>> --- a/kernel/module/main.c >>> +++ b/kernel/module/main.c >>> @@ -1053,6 +1053,7 @@ int try_to_force_load(struct module *mod, const char *reason) >>> add_taint_module(mod, TAINT_FORCED_MODULE, LOCKDEP_NOW_UNRELIABLE); >>> return 0; >>> #else >>> + pr_err("%s: %s\n", mod->name, reason); >>> return -ENOEXEC; >>> #endif >>> } >>> diff --git a/kernel/module/version.c b/kernel/module/version.c >>> index 2beefeba82d9..4d9ebf0834de 100644 >>> --- a/kernel/module/version.c >>> +++ b/kernel/module/version.c >>> @@ -41,9 +41,9 @@ int check_version(const struct load_info *info, >>> return 1; >>> } >>> - /* No versions at all? modprobe --force does this. */ >>> + /* No versions? Ok, already tainted in check_modstruct_version(). */ >>> if (versindex == 0) >>> - return try_to_force_load(mod, symname) == 0; >>> + return 1; >>> versions = (void *)sechdrs[versindex].sh_addr; >>> num_versions = sechdrs[versindex].sh_size >>> @@ -90,6 +90,11 @@ int check_modstruct_version(const struct load_info *info, >>> have_symbol = find_symbol(&fsa); >>> BUG_ON(!have_symbol); >>> + /* No versions at all? modprobe --force does this. */ >>> + if (!info->index.vers && !info->index.vers_ext_crc) >>> + return try_to_force_load( >>> + mod, "no versions for imported symbols") == 0; >>> + >>> return check_version(info, "module_layout", mod, fsa.crc); >>> } >>> >>> As a side note, I'm confused why with CONFIG_MODULE_FORCE_LOAD=y, the >>> code treats missing modversions for imported symbols as ok, even without >>> MODULE_INIT_IGNORE_MODVERSIONS. This is at least consistent with the >>> handling of missing vermagic, but it seems this behavior should be >>> stricter. >>> >> When debugging syzkaller, I noticed that the insmod command always reports errors. However, to get the exact information, I need to trace the kernel, so I casually submitted this patch. >> >> Based on your response, I also feel that the meaning of force_load here is somewhat unclear. It would be better to create a mask or a clear list to indicate which fields can be forced and which cannot. Once this is clear, we can create a function named may_force_check(). > > I cannot find an explicit reason in the Git history why a missing > vermagic is treated as if the module was loaded with > MODULE_INIT_IGNORE_VERMAGIC, and similarly why missing modversions data > is treated as if the module was loaded with > MODULE_INIT_IGNORE_MODVERSIONS. > > I would argue that a more sensible behavior would be to consider > a missing vermagic as an error and allow loading the module only if > MODULE_INIT_IGNORE_VERMAGIC is explicitly specified. And analogously for > missing modversions and MODULE_INIT_IGNORE_MODVERSIONS. > > Nonetheless, if I understand correctly, this should be mostly separate > from your issue. To answer my own confusion, the thing that I missed is that the MODULE_INIT_IGNORE_* flags are available only for the finit_module syscall, not for init_module. In the case of init_module, the force logic is handled by kmod in userspace by stripping the relevant modversions and vermagic data. This means that when using init_module, the module loader cannot distinguish between a module that lacks this data and one that has it deliberately removed. When finit_module was introduced in 2012, commit 2f3238aebedb ("module: add flags arg to sys_finit_module()") added the MODULE_INIT_IGNORE_* flags, and they were simply implemented to mirror the kmod behavior. -- Petr