[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <07ca17dce4638f11587da0ebd42bfc0533978298.camel@sipsolutions.net>
Date: Wed, 04 Dec 2024 15:04:12 +0100
From: Benjamin Berg <benjamin@...solutions.net>
To: jeffxu@...omium.org, akpm@...ux-foundation.org, keescook@...omium.org,
jannh@...gle.com, torvalds@...ux-foundation.org,
adhemerval.zanella@...aro.org, oleg@...hat.com,
linux-um@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
linux-mm@...ck.org, jorgelo@...omium.org, sroettger@...gle.com,
ojeda@...nel.org, adobriyan@...il.com, anna-maria@...utronix.de,
mark.rutland@....com, linus.walleij@...aro.org, Jason@...c4.com,
deller@....de, rdunlap@...radead.org, davem@...emloft.net, hch@....de,
peterx@...hat.com, hca@...ux.ibm.com, f.fainelli@...il.com,
gerg@...nel.org, dave.hansen@...ux.intel.com, mingo@...nel.org,
ardb@...nel.org, Liam.Howlett@...cle.com, mhocko@...e.com,
42.hyeyoo@...il.com, peterz@...radead.org, ardb@...gle.com, enh@...gle.com,
rientjes@...gle.com, groeck@...omium.org, mpe@...erman.id.au
Subject: Re: [PATCH v4 1/1] exec: seal system mappings
Hi,
On Mon, 2024-11-25 at 20:20 +0000, jeffxu@...omium.org wrote:
> From: Jeff Xu <jeffxu@...omium.org>
>
> 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.
Benjamin
[1] Hmm, we should mseal() those stub pages.
>
> 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@mail.gmail.com/
> Signed-off-by: Jeff Xu <jeffxu@...omium.org>
> ---
> .../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@...omium.org>
> */
>
> +#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
Powered by blists - more mailing lists