Messages in this thread |  | | Date | Mon, 22 Feb 2021 12:24:38 +0530 | From | pnagar@codeauro ... | Subject | Re: [PATCH] RTIC: selinux: ARM64: Move selinux_state to a separate page |
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On 2021-02-16 23:39, Nick Desaulniers wrote: > On Tue, Feb 16, 2021 at 2:19 AM Preeti Nagar <pnagar@codeaurora.org> > wrote: >> >> The changes introduce a new security feature, RunTime Integrity Check >> (RTIC), designed to protect Linux Kernel at runtime. The motivation >> behind these changes is: >> 1. The system protection offered by Security Enhancements(SE) for >> Android relies on the assumption of kernel integrity. If the kernel >> itself is compromised (by a perhaps as yet unknown future >> vulnerability), >> SE for Android security mechanisms could potentially be disabled and >> rendered ineffective. >> 2. Qualcomm Snapdragon devices use Secure Boot, which adds >> cryptographic >> checks to each stage of the boot-up process, to assert the >> authenticity >> of all secure software images that the device executes. However, due >> to >> various vulnerabilities in SW modules, the integrity of the system can >> be >> compromised at any time after device boot-up, leading to un-authorized >> SW executing. >> >> The feature's idea is to move some sensitive kernel structures to a >> separate page and monitor further any unauthorized changes to these, >> from higher Exception Levels using stage 2 MMU. Moving these to a >> different page will help avoid getting page faults from un-related >> data. >> The mechanism we have been working on removes the write permissions >> for >> HLOS in the stage 2 page tables for the regions to be monitored, such >> that any modification attempts to these will lead to faults being >> generated and handled by handlers. If the protected assets are moved >> to >> a separate page, faults will be generated corresponding to change >> attempts >> to these assets only. If not moved to a separate page, write attempts >> to >> un-related data present on the monitored pages will also be generated. >> >> Using this feature, some sensitive variables of the kernel which are >> initialized after init or are updated rarely can also be protected >> from >> simple overwrites and attacks trying to modify these. >> >> Currently, the change moves selinux_state structure to a separate >> page. >> The page is 2MB aligned not 4K to avoid TLB related performance impact >> as, >> for some CPU core designs, the TLB does not cache 4K stage 2 (IPA to >> PA) >> mappings if the IPA comes from a stage 1 mapping. In future, we plan >> to >> move more security-related kernel assets to this page to enhance >> protection. >> >> Signed-off-by: Preeti Nagar <pnagar@codeaurora.org> > > This addresses my feedback from the RFC regarding the section symbols. > No comment on whether there is a better approach, or the 2MB vs page > alignment, but perhaps other folks cc'ed can please take a look. > > Acked-by: Nick Desaulniers <ndesaulniers@google.com> > Thank you! I look forward to reviews and suggestions from the added folks.
>> --- >> The RFC patch reviewed available at: >> https://lore.kernel.org/linux-security-module/1610099389-28329-1-git-send-email-pnagar@codeaurora.org/ >> --- >> include/asm-generic/vmlinux.lds.h | 10 ++++++++++ >> include/linux/init.h | 6 ++++++ >> security/Kconfig | 11 +++++++++++ >> security/selinux/hooks.c | 2 +- >> 4 files changed, 28 insertions(+), 1 deletion(-) >> >> diff --git a/include/asm-generic/vmlinux.lds.h >> b/include/asm-generic/vmlinux.lds.h >> index b97c628..d1a5434 100644 >> --- a/include/asm-generic/vmlinux.lds.h >> +++ b/include/asm-generic/vmlinux.lds.h >> @@ -770,6 +770,15 @@ >> *(.scommon) >> \ >> } >> >> +#ifdef CONFIG_SECURITY_RTIC >> +#define RTIC_BSS >> \ >> + . = ALIGN(SZ_2M); >> \ >> + KEEP(*(.bss.rtic)) >> \ >> + . = ALIGN(SZ_2M); >> +#else >> +#define RTIC_BSS >> +#endif >> + >> /* >> * Allow archectures to redefine BSS_FIRST_SECTIONS to add extra >> * sections to the front of bss. >> @@ -782,6 +791,7 @@ >> . = ALIGN(bss_align); >> \ >> .bss : AT(ADDR(.bss) - LOAD_OFFSET) { >> \ >> BSS_FIRST_SECTIONS >> \ >> + RTIC_BSS >> \ >> . = ALIGN(PAGE_SIZE); >> \ >> *(.bss..page_aligned) >> \ >> . = ALIGN(PAGE_SIZE); >> \ >> diff --git a/include/linux/init.h b/include/linux/init.h >> index e668832..e6d452a 100644 >> --- a/include/linux/init.h >> +++ b/include/linux/init.h >> @@ -300,6 +300,12 @@ void __init parse_early_options(char *cmdline); >> /* Data marked not to be saved by software suspend */ >> #define __nosavedata __section(".data..nosave") >> >> +#ifdef CONFIG_SECURITY_RTIC >> +#define __rticdata __section(".bss.rtic") >> +#else >> +#define __rticdata >> +#endif >> + >> #ifdef MODULE >> #define __exit_p(x) x >> #else >> diff --git a/security/Kconfig b/security/Kconfig >> index 7561f6f..1af913a 100644 >> --- a/security/Kconfig >> +++ b/security/Kconfig >> @@ -291,5 +291,16 @@ config LSM >> >> source "security/Kconfig.hardening" >> >> +config SECURITY_RTIC >> + bool "RunTime Integrity Check feature" >> + depends on ARM64 >> + help >> + RTIC(RunTime Integrity Check) feature is to protect Linux >> kernel >> + at runtime. This relocates some of the security sensitive >> kernel >> + structures to a separate RTIC specific page. >> + >> + This is to enable monitoring and protection of these kernel >> assets >> + from a higher exception level(EL) against any unauthorized >> changes. >> + >> endmenu >> >> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c >> index 644b17e..59d7eee 100644 >> --- a/security/selinux/hooks.c >> +++ b/security/selinux/hooks.c >> @@ -104,7 +104,7 @@ >> #include "audit.h" >> #include "avc_ss.h" >> >> -struct selinux_state selinux_state; >> +struct selinux_state selinux_state __rticdata; >> >> /* SECMARK reference count */ >> static atomic_t selinux_secmark_refcount = ATOMIC_INIT(0); >> -- >> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a >> member >> of Code Aurora Forum, hosted by The Linux Foundation >>
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