On Wed, Dec 4, 2024 at 6:04 AM Benjamin Berg <benjamin@xxxxxxxxxxxxxxxx> wrote: > > Hi, > > On Mon, 2024-11-25 at 20:20 +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 [2]. 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. > > I think that enabling this feature would break User Mode Linux (UML). > It uses a tiny static helper executable to create userspace MMs. This > executable just maps some "stub" data/code pages[1] for management and > after that all other memory has to be unmapped as it is managed by the > UML kernel. > This unmapping will not work if the vdso/vvar mappings are sealed. > > Maybe nobody who enables the feature cares about UML. But wanted to > raise it as a potential issue in case you are not aware yet. > Thank you for bringing this to attention, I will add this information to documentation/comments. Do you think we need to add a KCONFIG check similar to !CHECKPOINT_RESTORE ? or this is something purely in userspace and the kernel doesn't have a control. > Benjamin > > [1] Hmm, we should mseal() those stub pages. > is this reference [1] correct ? > > > > Currently, memory sealing is only functional in a 64-bit kernel > > configuration. > > > > To enable this feature, the architecture needs to be tested to > > confirm that it doesn't unmap/remap system mappings during the > > the life time of the process. After the architecture enables > > ARCH_HAS_SEAL_SYSTEM_MAPPINGS, a distribution can set > > CONFIG_SEAL_SYSTEM_MAPPING to manage access to the feature. > > Alternatively, kernel command line (exec.seal_system_mappings) > > enables this feature also. > > > > This feature is tested using ChromeOS and Android on X86_64 and ARM64, > > therefore ARCH_HAS_SEAL_SYSTEM_MAPPINGS is set for X86_64 and ARM64. > > Other architectures can enable this after testing. No specific hardware > > features from the CPU are needed. > > > > This feature's security enhancements will benefit ChromeOS, Android, > > and other secure-by-default systems. > > > > [1] Documentation/userspace-api/mseal.rst > > [2] https://lore.kernel.org/all/CABi2SkU9BRUnqf70-nksuMCQ+yyiWjo3fM4XkRkL-NrCZxYAyg@xxxxxxxxxxxxxx/ > > Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > --- > > .../admin-guide/kernel-parameters.txt | 11 ++++++ > > Documentation/userspace-api/mseal.rst | 4 ++ > > arch/arm64/Kconfig | 1 + > > arch/x86/Kconfig | 1 + > > arch/x86/entry/vsyscall/vsyscall_64.c | 8 +++- > > include/linux/mm.h | 12 ++++++ > > init/Kconfig | 25 ++++++++++++ > > mm/mmap.c | 10 +++++ > > mm/mseal.c | 39 +++++++++++++++++++ > > security/Kconfig | 24 ++++++++++++ > > 10 files changed, 133 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index e7bfe1bde49e..f63268341739 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1538,6 +1538,17 @@ > > 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. > > + - 'no': do not seal system mappings. > > + - 'yes': seal system mappings. > > + This overrides CONFIG_SEAL_SYSTEM_MAPPINGS=(y/n) > > + If not specified or invalid, default is the value set by > > + CONFIG_SEAL_SYSTEM_MAPPINGS. > > + This option has no effect if CONFIG_64BIT=n > > + > > 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/Documentation/userspace-api/mseal.rst b/Documentation/userspace-api/mseal.rst > > index 41102f74c5e2..bec122318a59 100644 > > --- a/Documentation/userspace-api/mseal.rst > > +++ b/Documentation/userspace-api/mseal.rst > > @@ -130,6 +130,10 @@ Use cases > > > > - Chrome browser: protect some security sensitive data structures. > > > > +- seal system mappings: > > + kernel config CONFIG_SEAL_SYSTEM_MAPPINGS seals system mappings such > > + as vdso, vvar, sigpage, uprobes and vsyscall. > > + > > When not to use mseal > > ===================== > > Applications can apply sealing to any virtual memory region from userspace, > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 63de71544d95..fc5da8f74342 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -44,6 +44,7 @@ config ARM64 > > select ARCH_HAS_SETUP_DMA_OPS > > select ARCH_HAS_SET_DIRECT_MAP > > select ARCH_HAS_SET_MEMORY > > + select ARCH_HAS_SEAL_SYSTEM_MAPPINGS > > select ARCH_STACKWALK > > select ARCH_HAS_STRICT_KERNEL_RWX > > select ARCH_HAS_STRICT_MODULE_RWX > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 1ea18662942c..5f6bac99974c 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -26,6 +26,7 @@ config X86_64 > > depends on 64BIT > > # Options that are inherently 64-bit kernel only: > > select ARCH_HAS_GIGANTIC_PAGE > > + select ARCH_HAS_SEAL_SYSTEM_MAPPINGS > > select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 > > select ARCH_SUPPORTS_PER_VMA_LOCK > > select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE > > diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c > > index 2fb7d53cf333..30e0958915ca 100644 > > --- a/arch/x86/entry/vsyscall/vsyscall_64.c > > +++ b/arch/x86/entry/vsyscall/vsyscall_64.c > > @@ -366,8 +366,12 @@ 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); > > + } > > > > 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/init/Kconfig b/init/Kconfig > > index 1aa95a5dfff8..614719259aa0 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -1860,6 +1860,31 @@ config ARCH_HAS_MEMBARRIER_CALLBACKS > > config ARCH_HAS_MEMBARRIER_SYNC_CORE > > bool > > > > +config ARCH_HAS_SEAL_SYSTEM_MAPPINGS > > + bool > > + help > > + Control SEAL_SYSTEM_MAPPINGS access based on architecture. > > + > > + A 64-bit kernel is required for the memory sealing feature. > > + No specific hardware features from the CPU are needed. > > + > > + To enable this feature, the architecture needs to be tested to > > + confirm that it doesn't unmap/remap system mappings during the > > + the life time of the process. After the architecture enables this, > > + a distribution can set CONFIG_SEAL_SYSTEM_MAPPING to manage access > > + to the feature. > > + > > + The CONFIG_SEAL_SYSTEM_MAPPINGS already checks the CHECKPOINT_RESTORE > > + feature, which is known to remap/unmap vdso. Thus, the presence of > > + CHECKPOINT_RESTORE is not considered a factor in enabling > > + ARCH_HAS_SEAL_SYSTEM_MAPPINGS for a architecture. > > + > > + For complete list of system mappings, please see > > + CONFIG_SEAL_SYSTEM_MAPPINGS. > > + > > + For complete descriptions of memory sealing, please see > > + Documentation/userspace-api/mseal.rst > > + > > config HAVE_PERF_EVENTS > > bool > > help > > 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. > > + */ > > + 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..80126d6231bb 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 override 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..5bbb8d989d79 100644 > > --- a/security/Kconfig > > +++ b/security/Kconfig > > @@ -51,6 +51,30 @@ config PROC_MEM_NO_FORCE > > > > endchoice > > > > +config SEAL_SYSTEM_MAPPINGS > > + bool "seal system mappings" > > + default n > > + depends on 64BIT > > + depends on ARCH_HAS_SEAL_SYSTEM_MAPPINGS > > + depends on !CHECKPOINT_RESTORE > > + help > > + Seal system mappings such as vdso, vvar, sigpage, vsyscall, uprobes. > > + > > + A 64-bit kernel is required for the memory sealing feature. > > + No specific hardware features from the CPU are needed. > > + > > + Depends on the ARCH_HAS_SEAL_SYSTEM_MAPPINGS. > > + > > + CHECKPOINT_RESTORE might relocate vdso mapping during restore, > > + and remap/unmap will fail when the mapping is sealed, therefore > > + !CHECKPOINT_RESTORE is added as dependency. > > + > > + Kernel command line exec.seal_system_mappings=(no/yes) overrides > > + this. > > + > > + For complete descriptions of memory sealing, please see > > + Documentation/userspace-api/mseal.rst > > + > > config SECURITY > > bool "Enable different security models" > > depends on SYSFS > >
