Add an interface to the misc cgroup controller that allows masking out hardware capabilities (AT_HWCAP) reported to user-space processes. This provides a mechanism to restrict the features a containerized application can see. The new "misc.mask" cgroup file allows users to specify masks for AT_HWCAP, AT_HWCAP2, AT_HWCAP3, and AT_HWCAP4. The output of "misc.mask" is extended to display the effective mask, which is a combination of the masks from the current cgroup and all its ancestors. Signed-off-by: Andrei Vagin --- fs/binfmt_elf.c | 24 +++++-- include/linux/misc_cgroup.h | 25 +++++++ kernel/cgroup/misc.c | 126 ++++++++++++++++++++++++++++++++++++ 3 files changed, 171 insertions(+), 4 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 3eb734c192e9..59137784e81d 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -47,6 +47,7 @@ #include #include #include +#include #include #include @@ -182,6 +183,21 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, int ei_index; const struct cred *cred = current_cred(); struct vm_area_struct *vma; + struct misc_cg *misc_cg; + u64 hwcap_mask[4] = {0, 0, 0, 0}; + + misc_cg = get_current_misc_cg(); + misc_cg_get_mask(MISC_CG_MASK_HWCAP, misc_cg, &hwcap_mask[0]); +#ifdef ELF_HWCAP2 + misc_cg_get_mask(MISC_CG_MASK_HWCAP2, misc_cg, &hwcap_mask[1]); +#endif +#ifdef ELF_HWCAP3 + misc_cg_get_mask(MISC_CG_MASK_HWCAP3, misc_cg, &hwcap_mask[2]); +#endif +#ifdef ELF_HWCAP4 + misc_cg_get_mask(MISC_CG_MASK_HWCAP4, misc_cg, &hwcap_mask[3]); +#endif + put_misc_cg(misc_cg); /* * In some cases (e.g. Hyper-Threading), we want to avoid L1 @@ -246,7 +262,7 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, */ ARCH_DLINFO; #endif - NEW_AUX_ENT(AT_HWCAP, ELF_HWCAP); + NEW_AUX_ENT(AT_HWCAP, ELF_HWCAP & ~hwcap_mask[0]); NEW_AUX_ENT(AT_PAGESZ, ELF_EXEC_PAGESIZE); NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC); NEW_AUX_ENT(AT_PHDR, phdr_addr); @@ -264,13 +280,13 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, NEW_AUX_ENT(AT_SECURE, bprm->secureexec); NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes); #ifdef ELF_HWCAP2 - NEW_AUX_ENT(AT_HWCAP2, ELF_HWCAP2); + NEW_AUX_ENT(AT_HWCAP2, ELF_HWCAP2 & ~hwcap_mask[1]); #endif #ifdef ELF_HWCAP3 - NEW_AUX_ENT(AT_HWCAP3, ELF_HWCAP3); + NEW_AUX_ENT(AT_HWCAP3, ELF_HWCAP3 & ~hwcap_mask[2]); #endif #ifdef ELF_HWCAP4 - NEW_AUX_ENT(AT_HWCAP4, ELF_HWCAP4); + NEW_AUX_ENT(AT_HWCAP4, ELF_HWCAP4 & ~hwcap_mask[3]); #endif NEW_AUX_ENT(AT_EXECFN, bprm->exec); if (k_platform) { diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h index 0cb36a3ffc47..cff830c238fb 100644 --- a/include/linux/misc_cgroup.h +++ b/include/linux/misc_cgroup.h @@ -8,6 +8,8 @@ #ifndef _MISC_CGROUP_H_ #define _MISC_CGROUP_H_ +#include + /** * enum misc_res_type - Types of misc cgroup entries supported by the host. */ @@ -26,6 +28,20 @@ enum misc_res_type { MISC_CG_RES_TYPES }; +enum misc_mask_type { + MISC_CG_MASK_HWCAP, +#ifdef ELF_HWCAP2 + MISC_CG_MASK_HWCAP2, +#endif +#ifdef ELF_HWCAP3 + MISC_CG_MASK_HWCAP3, +#endif +#ifdef ELF_HWCAP4 + MISC_CG_MASK_HWCAP4, +#endif + MISC_CG_MASK_TYPES +}; + struct misc_cg; #ifdef CONFIG_CGROUP_MISC @@ -62,12 +78,15 @@ struct misc_cg { struct cgroup_file events_local_file; struct misc_res res[MISC_CG_RES_TYPES]; + u64 mask[MISC_CG_MASK_TYPES]; }; int misc_cg_set_capacity(enum misc_res_type type, u64 capacity); int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg, u64 amount); void misc_cg_uncharge(enum misc_res_type type, struct misc_cg *cg, u64 amount); +int misc_cg_get_mask(enum misc_mask_type type, struct misc_cg *cg, u64 *pmask); + /** * css_misc() - Get misc cgroup from the css. * @css: cgroup subsys state object. @@ -134,5 +153,11 @@ static inline void put_misc_cg(struct misc_cg *cg) { } +static inline int misc_cg_get_mask(enum misc_mask_type type, struct misc_cg *cg, u64 *pmask) +{ + *pmask = 0; + return 0; +} + #endif /* CONFIG_CGROUP_MISC */ #endif /* _MISC_CGROUP_H_ */ diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c index 6a01d91ea4cb..d1386d86060f 100644 --- a/kernel/cgroup/misc.c +++ b/kernel/cgroup/misc.c @@ -30,6 +30,19 @@ static const char *const misc_res_name[] = { #endif }; +static const char *const misc_mask_name[] = { + "AT_HWCAP", +#ifdef ELF_HWCAP2 + "AT_HWCAP2", +#endif +#ifdef ELF_HWCAP3 + "AT_HWCAP3", +#endif +#ifdef ELF_HWCAP4 + "AT_HWCAP4", +#endif +}; + /* Root misc cgroup */ static struct misc_cg root_cg; @@ -71,6 +84,11 @@ static inline bool valid_type(enum misc_res_type type) return type >= 0 && type < MISC_CG_RES_TYPES; } +static inline bool valid_mask_type(enum misc_mask_type type) +{ + return type >= 0 && type < MISC_CG_MASK_TYPES; +} + /** * misc_cg_set_capacity() - Set the capacity of the misc cgroup res. * @type: Type of the misc res. @@ -391,6 +409,109 @@ static int misc_events_local_show(struct seq_file *sf, void *v) return __misc_events_show(sf, true); } +/** + * misc_cg_get_mask() - Get the mask of the specified type. + * @type: The misc mask type. + * @cg: The misc cgroup. + * @pmask: Pointer to the resulting mask. + * + * This function calculates the effective mask for a given cgroup by walking up + * the hierarchy and ORing the masks from all parent cgroupfs. The final result + * is stored in the location pointed to by @pmask. + * + * Context: Any context. + * Return: 0 on success, -EINVAL if @type is invalid. + */ +int misc_cg_get_mask(enum misc_mask_type type, struct misc_cg *cg, u64 *pmask) +{ + struct misc_cg *i; + u64 mask = 0; + + if (!(valid_mask_type(type))) + return -EINVAL; + + for (i = cg; i; i = parent_misc(i)) + mask |= READ_ONCE(i->mask[type]); + + *pmask = mask; + return 0; +} + +/** + * misc_cg_mask_show() - Show the misc cgroup masks. + * @sf: Interface file + * @v: Arguments passed + * + * Context: Any context. + * Return: 0 to denote successful print. + */ +static int misc_cg_mask_show(struct seq_file *sf, void *v) +{ + struct misc_cg *cg = css_misc(seq_css(sf)); + int i; + + for (i = 0; i < MISC_CG_MASK_TYPES; i++) { + u64 rval, val = READ_ONCE(cg->mask[i]); + + misc_cg_get_mask(i, cg, &rval); + seq_printf(sf, "%s\t%#016llx\t%#016llx\n", misc_mask_name[i], val, rval); + } + + return 0; +} + +/** + * misc_cg_mask_write() - Update the mask of the specified type. + * @of: Handler for the file. + * @buf: The buffer containing the user's input. + * @nbytes: The number of bytes in @buf. + * @off: The offset in the file. + * + * This function parses a user-provided string to update a mask. + * The expected format is " ", for example: + * + * echo "AT_HWCAP 0xf00" > misc.mask + * + * Context: Process context. + * Return: The number of bytes processed on success, or a negative error code + * on failure. + */ +static ssize_t misc_cg_mask_write(struct kernfs_open_file *of, char *buf, + size_t nbytes, loff_t off) +{ + struct misc_cg *cg; + u64 max; + int ret = 0, i; + enum misc_mask_type type = MISC_CG_MASK_TYPES; + char *token; + + buf = strstrip(buf); + token = strsep(&buf, " "); + + if (!token || !buf) + return -EINVAL; + + for (i = 0; i < MISC_CG_MASK_TYPES; i++) { + if (!strcmp(misc_mask_name[i], token)) { + type = i; + break; + } + } + + if (type == MISC_CG_MASK_TYPES) + return -EINVAL; + + ret = kstrtou64(buf, 0, &max); + if (ret) + return ret; + + cg = css_misc(of_css(of)); + + WRITE_ONCE(cg->mask[type], max); + + return nbytes; +} + /* Misc cgroup interface files */ static struct cftype misc_cg_files[] = { { @@ -424,6 +545,11 @@ static struct cftype misc_cg_files[] = { .file_offset = offsetof(struct misc_cg, events_local_file), .seq_show = misc_events_local_show, }, + { + .name = "mask", + .write = misc_cg_mask_write, + .seq_show = misc_cg_mask_show, + }, {} }; -- 2.52.0.223.gf5cc29aaa4-goog