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path: root/include/linux/scs.h
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2022-11-09scs: add support for dynamic shadow call stacksArd Biesheuvel1-0/+18
In order to allow arches to use code patching to conditionally emit the shadow stack pushes and pops, rather than always taking the performance hit even on CPUs that implement alternatives such as stack pointer authentication on arm64, add a Kconfig symbol that can be set by the arch to omit the SCS codegen itself, without otherwise affecting how support code for SCS and compiler options (for register reservation, for instance) are emitted. Also, add a static key and some plumbing to omit the allocation of shadow call stack for dynamic SCS configurations if SCS is disabled at runtime. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Tested-by: Sami Tolvanen <samitolvanen@google.com> Link: https://lore.kernel.org/r/20221027155908.1940624-3-ardb@kernel.org Signed-off-by: Will Deacon <will@kernel.org>
2020-12-01arm64: scs: use vmapped IRQ and SDEI shadow stacksSami Tolvanen1-4/+0
Use scs_alloc() to allocate also IRQ and SDEI shadow stacks instead of using statically allocated stacks. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201130233442.2562064-3-samitolvanen@google.com [will: Move CONFIG_SHADOW_CALL_STACK check into init_irq_scs()] Signed-off-by: Will Deacon <will@kernel.org>
2020-12-01scs: switch to vmapped shadow stacksSami Tolvanen1-6/+6
The kernel currently uses kmem_cache to allocate shadow call stacks, which means an overflows may not be immediately detected and can potentially result in another task's shadow stack to be overwritten. This change switches SCS to use virtually mapped shadow stacks for tasks, which increases shadow stack size to a full page and provides more robust overflow detection, similarly to VMAP_STACK. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201130233442.2562064-2-samitolvanen@google.com Signed-off-by: Will Deacon <will@kernel.org>
2020-05-18scs: Move DEFINE_SCS macro into core codeWill Deacon1-0/+4
Defining static shadow call stacks is not architecture-specific, so move the DEFINE_SCS() macro into the core header file. Tested-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will@kernel.org>
2020-05-18scs: Move scs_overflow_check() out of architecture codeWill Deacon1-2/+2
There is nothing architecture-specific about scs_overflow_check() as it's just a trivial wrapper around scs_corrupted(). For parity with task_stack_end_corrupted(), rename scs_corrupted() to task_scs_end_corrupted() and call it from schedule_debug() when CONFIG_SCHED_STACK_END_CHECK_is enabled, which better reflects its purpose as a debug feature to catch inadvertent overflow of the SCS. Finally, remove the unused scs_overflow_check() function entirely. This has absolutely no impact on architectures that do not support SCS (currently arm64 only). Tested-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will@kernel.org>
2020-05-18arm64: scs: Store absolute SCS stack pointer value in thread_infoWill Deacon1-4/+4
Storing the SCS information in thread_info as a {base,offset} pair introduces an additional load instruction on the ret-to-user path, since the SCS stack pointer in x18 has to be converted back to an offset by subtracting the base. Replace the offset with the absolute SCS stack pointer value instead and avoid the redundant load. Tested-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will@kernel.org>
2020-05-15scs: Add support for Clang's Shadow Call Stack (SCS)Sami Tolvanen1-0/+68
This change adds generic support for Clang's Shadow Call Stack, which uses a shadow stack to protect return addresses from being overwritten by an attacker. Details are available here: https://clang.llvm.org/docs/ShadowCallStack.html Note that security guarantees in the kernel differ from the ones documented for user space. The kernel must store addresses of shadow stacks in memory, which means an attacker capable reading and writing arbitrary memory may be able to locate them and hijack control flow by modifying the stacks. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> [will: Numerous cosmetic changes] Signed-off-by: Will Deacon <will@kernel.org>