I'd prefer not to move forward with this until we have confirmation that adequate testing has been performed, given how invasive this change is, even if behind a flag (unless we explicitly mention it is untested in the Kconfig). We are touching arch-specific stuff with VDSO, VVAR, etc. so we need to be cautious when we're in effect hooking an arch-specific function in mm. Other than that, the actual patch isn't too crazy overall. I think a sensible approach might be to only enable on known-good arches. On Wed, Nov 13, 2024 at 07:16:02PM +0000, jeffxu@xxxxxxxxxxxx wrote: > From: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > Seal vdso, vvar, sigpage, uprobes and vsyscall. > > Those mappings are readonly or executable only, sealing can protect > them from ever changing or unmapped during the life time of the process. > For complete descriptions of memory sealing, please see mseal.rst [1]. > > System mappings such as vdso, vvar, and sigpage (for arm) are > generated by the kernel during program initialization, and are > sealed after creation. > > Unlike the aforementioned mappings, the uprobe mapping is not > established during program startup. However, its lifetime is the same > as the process's lifetime [1]. It is sealed from creation. > > The vdso, vvar, sigpage, and uprobe mappings all invoke the > _install_special_mapping() function. As no other mappings utilize this > function, it is logical to incorporate sealing logic within > _install_special_mapping(). This approach avoids the necessity of > modifying code across various architecture-specific implementations. > > The vsyscall mapping, which has its own initialization function, is > sealed in the XONLY case, it seems to be the most common and secure > case of using vsyscall. > > It is important to note that the CHECKPOINT_RESTORE feature (CRIU) may > alter the mapping of vdso, vvar, and sigpage during restore > operations. Consequently, this feature cannot be universally enabled > across all systems. To address this, a kernel configuration option has > been introduced to enable or disable this functionality. > > [1] Documentation/userspace-api/mseal.rst It'd be nice to explicitly refer to this in the docs, it's not quite urgent though would be nice to be part of this series. > [2] https://lore.kernel.org/all/CABi2SkU9BRUnqf70-nksuMCQ+yyiWjo3fM4XkRkL-NrCZxYAyg@xxxxxxxxxxxxxx/ > Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx> > --- > .../admin-guide/kernel-parameters.txt | 10 +++++ > arch/x86/entry/vsyscall/vsyscall_64.c | 9 ++++- > include/linux/mm.h | 12 ++++++ > mm/mmap.c | 10 +++++ > mm/mseal.c | 39 +++++++++++++++++++ > security/Kconfig | 11 ++++++ > 6 files changed, 89 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index e7bfe1bde49e..469a65b3cf50 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1538,6 +1538,16 @@ > Permit 'security.evm' to be updated regardless of > current integrity status. > > + exec.seal_system_mappings = [KNL] > + Format: { no | yes } > + Seal system mappings: vdso, vvar, sigpage, vsyscall, > + uprobe. > + This overwrites KCONFIG CONFIG_SEAL_SYSTEM_MAPPINGS > + - 'no': do not seal system mappings. > + - 'yes': seal system mappings. > + If not specified or invalid, default is the KCONFIG value. > + This option has no effect if CONFIG_64BIT=n Or if CONFIG_CHECKPOINT_RESTORE is not set. Please update to reference this also. > + > early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier > stages so cover more early boot allocations. > Please note that as side effect some optimizations > diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c > index 2fb7d53cf333..185553376f39 100644 > --- a/arch/x86/entry/vsyscall/vsyscall_64.c > +++ b/arch/x86/entry/vsyscall/vsyscall_64.c > @@ -366,8 +366,13 @@ void __init map_vsyscall(void) > set_vsyscall_pgtable_user_bits(swapper_pg_dir); > } > > - if (vsyscall_mode == XONLY) > - vm_flags_init(&gate_vma, VM_EXEC); > + if (vsyscall_mode == XONLY) { > + unsigned long vm_flags = VM_EXEC; > + > + vm_flags |= seal_system_mappings(); > + > + vm_flags_init(&gate_vma, vm_flags); Nit: remove weird whitespace above. Also might be worth adding a comment as to what we're doing here similar to the one in _install_special_mapping(). > + } > > BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != > (unsigned long)VSYSCALL_ADDR); > diff --git a/include/linux/mm.h b/include/linux/mm.h > index df0a5eac66b7..f787d6c85cbb 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4238,4 +4238,16 @@ int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *st > int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status); > int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > > +#ifdef CONFIG_64BIT > +/* > + * return VM_SEALED if seal system mapping is enabled. > + */ > +unsigned long seal_system_mappings(void); > +#else > +static inline unsigned long seal_system_mappings(void) > +{ > + return 0; > +} > +#endif > + > #endif /* _LINUX_MM_H */ > diff --git a/mm/mmap.c b/mm/mmap.c > index 57fd5ab2abe7..bc694c555805 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2133,6 +2133,16 @@ struct vm_area_struct *_install_special_mapping( > unsigned long addr, unsigned long len, > unsigned long vm_flags, const struct vm_special_mapping *spec) > { > + /* > + * At present, all mappings (vdso, vvar, sigpage, and uprobe) that > + * invoke the _install_special_mapping function can be sealed. > + * Therefore, it is logical to call the seal_system_mappings_enabled() > + * function here. In the future, if this is not the case, i.e. if certain > + * mappings cannot be sealed, then it would be necessary to move this > + * check to the calling function. > + */ Nice comment! > + vm_flags |= seal_system_mappings(); > + > return __install_special_mapping(mm, addr, len, vm_flags, (void *)spec, > &special_mapping_vmops); > } > diff --git a/mm/mseal.c b/mm/mseal.c > index ece977bd21e1..0a9d1e9faa28 100644 > --- a/mm/mseal.c > +++ b/mm/mseal.c > @@ -7,6 +7,7 @@ > * Author: Jeff Xu <jeffxu@xxxxxxxxxxxx> > */ > > +#include <linux/fs_parser.h> > #include <linux/mempolicy.h> > #include <linux/mman.h> > #include <linux/mm.h> > @@ -266,3 +267,41 @@ SYSCALL_DEFINE3(mseal, unsigned long, start, size_t, len, unsigned long, > { > return do_mseal(start, len, flags); > } > + > +/* > + * Kernel cmdline overwrite for CONFIG_SEAL_SYSTEM_MAPPINGS > + */ > +enum seal_system_mappings_type { > + SEAL_SYSTEM_MAPPINGS_DISABLED, > + SEAL_SYSTEM_MAPPINGS_ENABLED > +}; > + > +static enum seal_system_mappings_type seal_system_mappings_v __ro_after_init = > + IS_ENABLED(CONFIG_SEAL_SYSTEM_MAPPINGS) ? SEAL_SYSTEM_MAPPINGS_ENABLED : > + SEAL_SYSTEM_MAPPINGS_DISABLED; > + > +static const struct constant_table value_table_sys_mapping[] __initconst = { > + { "no", SEAL_SYSTEM_MAPPINGS_DISABLED}, > + { "yes", SEAL_SYSTEM_MAPPINGS_ENABLED}, > + { } > +}; > + > +static int __init early_seal_system_mappings_override(char *buf) > +{ > + if (!buf) > + return -EINVAL; > + > + seal_system_mappings_v = lookup_constant(value_table_sys_mapping, > + buf, seal_system_mappings_v); > + return 0; > +} > + > +early_param("exec.seal_system_mappings", early_seal_system_mappings_override); > + > +unsigned long seal_system_mappings(void) > +{ > + if (seal_system_mappings_v == SEAL_SYSTEM_MAPPINGS_ENABLED) > + return VM_SEALED; > + > + return 0; > +} > diff --git a/security/Kconfig b/security/Kconfig > index 28e685f53bd1..63b87a218943 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -51,6 +51,17 @@ config PROC_MEM_NO_FORCE > > endchoice > > +config SEAL_SYSTEM_MAPPINGS > + bool "seal system mappings" > + default n > + depends on 64BIT > + depends on !CHECKPOINT_RESTORE Would prefer to depend on actually tested architectures only. > + help > + Seal system mappings such as vdso, vvar, sigpage, vsyscall, uprobes. > + Note: CHECKPOINT_RESTORE might relocate vdso mapping during restore, > + and remap will fail if the mapping is sealed, therefore > + !CHECKPOINT_RESTORE is added as dependency. > + > config SECURITY > bool "Enable different security models" > depends on SYSFS > -- > 2.47.0.277.g8800431eea-goog >
