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| -rw-r--r-- | Base/usr/share/man/man7/Mitigations.md | 69 |
1 files changed, 32 insertions, 37 deletions
diff --git a/Base/usr/share/man/man7/Mitigations.md b/Base/usr/share/man/man7/Mitigations.md index eb01a4986d..bca5e8168e 100644 --- a/Base/usr/share/man/man7/Mitigations.md +++ b/Base/usr/share/man/man7/Mitigations.md @@ -1,6 +1,6 @@ ## Name -Mitigations - Security mitigations implemented by SerenityOS. +Mitigations - Security mitigations implemented by SerenityOS ## Description @@ -13,9 +13,8 @@ to collect and describe the mitigations in one centralized place. ### SMEP (Supervisor Mode Execution Protection) -[Supervisor Mode Execution Protection](https://software.intel.com/security-software-guidance/best-practices/related-intel-security-features-technologies) is a feature -of Intel CPUs which allows the kernel to instruct the CPU -to disable execution of code residing in user space. +[Supervisor Mode Execution Protection](https://software.intel.com/security-software-guidance/best-practices/related-intel-security-features-technologies) is an Intel CPU feature which prevents execution +of userspace code with kernel privileges. It was enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/8602fa5b49aa4e2b039764a14698f0baa3ad0532): ``` @@ -29,9 +28,9 @@ Kernel: Enable x86 SMEP (Supervisor Mode Execution Protection) ### SMAP (Supervisor Mode Access Prevention) -[Supervisor Mode Access Prevention](https://en.wikipedia.org/wiki/Supervisor_Mode_Access_Prevention) compliments -SMEP, it allows a kernel to set user-space memory mappings -that will cause a trap when accessing user-space memory. +[Supervisor Mode Access Prevention](https://en.wikipedia.org/wiki/Supervisor_Mode_Access_Prevention) +compliments SMEP by also guarding read/write access to +userspace memory while executing in kernel mode. It was enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/9eef39d68a99c5e29099ae4eb4a56934b35eecde): @@ -45,10 +44,9 @@ Kernel: Start implementing x86 SMAP support ### Pledge -[pledge](https://marc.info/?l=openbsd-tech&m=143725996614627&w=2) is a mitigation which originated from OpenBSD (originally named tame). -It enables a program to voluntarily restrict its access to the kernel's syscall -surface area. The allows the program to reduce the potential attack surface -available if the program in question was exploited. +[pledge](https://marc.info/?l=openbsd-tech&m=143725996614627&w=2) is a mitigation which originated from OpenBSD. +It allows a program to voluntarily restrict its access to system calls +and kernel facilities. It was first added in the following [commit](https://github.com/SerenityOS/serenity/commit/41c504a33becea8aa9b437cd3c0dc312b2bf1fe9), and the majority of programs were enlightened later: @@ -63,9 +61,8 @@ Kernel: Add pledge() syscall :^) ### Unveil -[unveil](https://lwn.net/Articles/767137/) is a mitigation which originated from OpenBSD. -It enables a program to voluntarily restrict its access to the filesystem. -This reduces the potential surface area available if the program in question was exploited. +[unveil](https://lwn.net/Articles/767137/) is a mitigation originating from OpenBSD. +It allows a program to voluntarily restrict its access to the filesystem. It was first added in the following [commit](https://github.com/SerenityOS/serenity/commit/0569123ad7cb9c54df724c2bb85933ea3cf97134), and the majority of programs were enlightened later: @@ -83,7 +80,7 @@ Kernel: Add a basic implementation of unveil() [syscall call-from verification](https://marc.info/?l=openbsd-tech&m=157488907117170&w=2) is a mitigation which originated from OpenBSD. In short the kernel checks that all syscalls originate -from the address of the systems libc. This makes attacks +from the address of the system's libc. This makes attacks on OpenBSD more difficult as they random-relink their libc on boot, which makes finding syscall stubs in libc difficult for attackers. On serenity it is mostly just an inconvenience, @@ -103,9 +100,9 @@ Kernel: Add a way to specify which memory regions can make syscalls [Post-init read-only memory](https://lwn.net/Articles/666550/) is a mitigation which originated from the Linux Kernel. -It tracks data that is initialized once during kernel boot and never -touched again, post kernel initialization the memory is marked -read only to protect it from potentially being modified by exploits. +It tracks data that is initialized during kernel boot and never +changed again. Post kernel initialization, the memory is marked +read-only to protect it from potentially being modified by exploits. It was first enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/d8013c60bb52756788e747183572067d6e3f204a) and other kernel data structures were enlightened later: @@ -120,11 +117,10 @@ Kernel: Add mechanism to make some memory read-only after init finishes ### KUBSAN (Kernel Undefined Behavior Sanitizer) -Undefined behavior sanitizer is a dynamic analysis tool, implemented in GCC, +UndefinedBehaviorSANitizer is a dynamic analysis tool, implemented in GCC, which instruments generated code to flag undefined behavior at runtime. -It can find various issues including, overflows, out of bounds array -accesses, type corruption, and many more. Undefined behavior bugs can often -be exploited, KUBSAN allows developers to catch them during testing instead. +It can find various issues, including integer overflows, out-of-bounds array +accesses, type corruption, and more. It was first enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/d44be968938ecf95023351a358c43c4957638d87): ``` @@ -135,11 +131,11 @@ Date: Fri Feb 5 19:44:26 2021 +0100 Kernel: KUBSAN! (Kernel Undefined Behavior SANitizer) :^) ``` -### Kernel Unmap after init +### Kernel unmap-after-init -Umap after init allows the kerenel to remove functions which contain potentially +Umap-after-init allows the kerenel to remove functions which contain potentially dangerous [ROP gadgets](https://en.wikipedia.org/wiki/Return-oriented_programming) -from kernel memory after they have been used and are no longer needed. Notably the +from kernel memory after we've booted up and they are no longer needed. Notably the `write_cr4(..)` function used to control processor features like the SMEP/SMAP bits in the CR4 register, and the `write_cr0(..)` function used to control processor features like write protection, etc. @@ -156,17 +152,16 @@ Date: Fri Feb 19 18:21:54 2021 +0100 Kernel: Add .unmap_after_init section for code we don't need after init ``` -### Reloaction Read-Only (RELRO) +### Relocation Read-Only (RELRO) [RELRO](https://hockeyinjune.medium.com/relro-relocation-read-only-c8d0933faef3) is a mitigation in the linker and loader that hardens the data sections of an ELF binary. -When linked with the relro option the resulting binary will have new sections emitted which -contain the relro data (`.data.rel.ro` and `.data.rel.ro.local`). The sections will be placed -into a program segment of type `PT_GNU_RELRO` which contains the relro sections. -The loader can then detect the `PT_GNU_RELRO` segment and then make the regions read only after -relocations have been performed. -This mitigates attacks which for example attempt to overwrite the [Global Offset Table (GOT)](https://en.wikipedia.org/wiki/Global_Offset_Table). +When enabled, it segregates function pointers resolved by the dynamic loader +into a separate section of the runtie executable memory, and allows the loader +to make that memory read-only before passing control to the main executable. + +This prevents attackers from overwriting the [Global Offset Table (GOT)](https://en.wikipedia.org/wiki/Global_Offset_Table). It was first enabled for executables in the following [commit](https://github.com/SerenityOS/serenity/commit/fa4c249425a65076ca04a3cb0c173d49472796fb): ``` @@ -177,7 +172,7 @@ Date: Thu Feb 18 18:43:20 2021 +0100 LibELF+Userland: Enable RELRO for all userland executables :^) ``` -Shared libraries were enabled in a folow up [commit](https://github.com/SerenityOS/serenity/commit/713b3b36be4f659e58e253b6c830509898dbd2fa): +Shared libraries were enabled in a follow-up [commit](https://github.com/SerenityOS/serenity/commit/713b3b36be4f659e58e253b6c830509898dbd2fa): ``` commit 713b3b36be4f659e58e253b6c830509898dbd2fa Author: Andreas Kling <kling@serenityos.org> @@ -190,8 +185,8 @@ DynamicLoader+Userland: Enable RELRO for shared libraries as well :^) The GCC compiler option [`-fstack-clash-protection`](https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html) is a mitigation which helps prevent [stack clash](https://blog.qualys.com/vulnerabilities-research/2017/06/19/the-stack-clash) -style attacks by generating code which allocates and immediately accesses one page of stack at a time. -This prevents attackers from creating situations in which stack allocations jump over a guard page into whatever lies after. +style attacks by generating code that probes the stack in page-sized increments to ensure a fault is provoked. +This prevents attackers from using a large stack allocation to "jump over" the stack guard page into adjacent memory. It was first enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/7142562310e631156d1f64aff22f068ae2c48a5e): ``` @@ -209,8 +204,8 @@ This family of flags enables [buffer overflow protection](https://en.wikipedia.o to mitigate [stack-smashing attacks](https://en.wikipedia.org/wiki/Stack_buffer_overflow). The compiler implements the mitigation by storing a canary value randomized on program startup into the preamble of all -functions. Code is then generated to check that stack canary on function return and crash if the value has been changed, -and hence a stack corruption has been detected. +functions. Code is then generated to validate that stack canary on function return and crash if the value has been changed +(and hence a stack corruption has been detected.) `-fstack-protector` was first enabled in the following [commit](https://github.com/SerenityOS/serenity/commit/842716a0b5eceb8db31416cd643720c1037032b2): |