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([2804:14c:4e1:8732:c479:1206:16fb:ce1f]) by smtp.gmail.com with ESMTPSA id k23-20020a056870959700b000f5f4ad194bsm1814528oao.25.2022.07.21.19.24.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Jul 2022 19:24:31 -0700 (PDT) From: Mauricio Faria de Oliveira To: linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: Masahiro Yamada , Michal Marek , Nick Desaulniers , Luis Chamberlain , Kees Cook , Iurii Zaikin Subject: [RFC PATCH 3/6] sysctl, mod_devicetable: shadow struct ctl_table.procname for file2alias Date: Thu, 21 Jul 2022 23:24:13 -0300 Message-Id: <20220722022416.137548-4-mfo@canonical.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220722022416.137548-1-mfo@canonical.com> References: <20220722022416.137548-1-mfo@canonical.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org In order to expose a sysctl entry to modpost (file2alias.c, precisely) we have to shadow 'struct ctl_table' in mod_devicetable.h, as scripts should not access kernel headers or its types (see file2alias.c). The required field is '.procname' (basename of '/proc/sys/.../entry'). Since 'struct ctl_table' is annotated for structure randomization and we need a known offset for '.procname' (remember, no kernel headers), take it out of the randomized portion (as in, eg, 'struct task_struct'). Of course, add build-time checks for struct size and .procname offset between both structs. (This has to be done on kernel side; for headers.) With that in place, use the regular macros in devicetable-offsets.c to define SIZE_... and OFF_... macros for the shadow struct and the field of interest. Signed-off-by: Mauricio Faria de Oliveira --- fs/proc/proc_sysctl.c | 19 +++++++++++++++++++ include/linux/mod_devicetable.h | 25 +++++++++++++++++++++++++ include/linux/sysctl.h | 11 ++++++++++- kernel/sysctl.c | 1 + scripts/mod/devicetable-offsets.c | 3 +++ 5 files changed, 58 insertions(+), 1 deletion(-) diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index 021e83fe831f..ebbf8702387e 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -19,6 +19,24 @@ #include #include "internal.h" +#ifdef CONFIG_MODULES +#include + +static void check_struct_sysctl_device_id(void) +{ + /* + * The shadow struct sysctl_device_id for file2alias.c needs + * the same size of struct ctl_table and offset for procname. + */ + BUILD_BUG_ON(sizeof(struct sysctl_device_id) + != sizeof(struct ctl_table)); + BUILD_BUG_ON(offsetof(struct sysctl_device_id, procname) + != offsetof(struct ctl_table, procname)); +} +#else +static void check_struct_sysctl_device_id(void) {} +#endif + #define list_for_each_table_entry(entry, table) \ for ((entry) = (table); (entry)->procname; (entry)++) @@ -1779,6 +1797,7 @@ int __init proc_sys_init(void) proc_sys_root->proc_dir_ops = &proc_sys_dir_file_operations; proc_sys_root->nlink = 0; + check_struct_sysctl_device_id(); return sysctl_init_bases(); } diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h index 549590e9c644..9cee024d8f2f 100644 --- a/include/linux/mod_devicetable.h +++ b/include/linux/mod_devicetable.h @@ -20,6 +20,31 @@ enum { PCI_ID_F_VFIO_DRIVER_OVERRIDE = 1, }; +/* + * "Device" table entry for a sysctl file (shadow of struct ctl_table). + * + * Only the procname field is reliable (known offset); all other fields + * are in the randomized portion of struct ctl_table, do NOT use them. + */ +struct sysctl_device_id { + + /* This must be the first field (shadowed from struct ctl_table). */ + const char *procname; + + /* Here begins the randomizable portion of struct ctl_table. */ + + void *data; + int maxlen; + unsigned short mode; // umode_t in + void *child; + void *proc_handler; + void *poll; + void *extra1; + void *extra2; + + /* Here ends the randomizable portion of struct ctl_table. */ +}; + /** * struct pci_device_id - PCI device ID structure * @vendor: Vendor ID to match (or PCI_ANY_ID) diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index 780690dc08cd..676112fde5ff 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -133,7 +133,13 @@ static inline void *proc_sys_poll_event(struct ctl_table_poll *poll) /* A sysctl table is an array of struct ctl_table: */ struct ctl_table { + + /* This must be the first field (shadowed to struct sysctl_device_id) */ const char *procname; /* Text ID for /proc/sys, or zero */ + + /* This begins the randomizable portion of the struct. */ + randomized_struct_fields_start + void *data; int maxlen; umode_t mode; @@ -142,7 +148,10 @@ struct ctl_table { struct ctl_table_poll *poll; void *extra1; void *extra2; -} __randomize_layout; + + /* New fields go above here, so they are in the randomized portion. */ + randomized_struct_fields_end +}; struct ctl_node { struct rb_node node; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 223376959d29..15073621cfa8 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -2487,6 +2487,7 @@ int __init sysctl_init_bases(void) return 0; } + #endif /* CONFIG_SYSCTL */ /* * No sense putting this after each symbol definition, twice, diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c index c0d3bcb99138..43b2549940d2 100644 --- a/scripts/mod/devicetable-offsets.c +++ b/scripts/mod/devicetable-offsets.c @@ -262,5 +262,8 @@ int main(void) DEVID(ishtp_device_id); DEVID_FIELD(ishtp_device_id, guid); + DEVID(sysctl_device_id); + DEVID_FIELD(sysctl_device_id, procname); + return 0; } -- 2.25.1