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authorArd Biesheuvel <ardb@kernel.org>2022-10-27 18:59:07 +0300
committerWill Deacon <will@kernel.org>2022-11-09 21:06:35 +0300
commit9beccca0984022a844850e32f0d7dd80d4a225de (patch)
treef9a9128498d40dee1958e15b212707872f039e38 /include/linux/scs.h
parent68c76ad4a9571a2b603665c85cf8229bcf04982a (diff)
downloadlinux-9beccca0984022a844850e32f0d7dd80d4a225de.tar.xz
scs: add support for dynamic shadow call stacks
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>
Diffstat (limited to 'include/linux/scs.h')
-rw-r--r--include/linux/scs.h18
1 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/scs.h b/include/linux/scs.h
index 18122d9e17ff..4ab5bdc898cf 100644
--- a/include/linux/scs.h
+++ b/include/linux/scs.h
@@ -53,6 +53,22 @@ static inline bool task_scs_end_corrupted(struct task_struct *tsk)
return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
}
+DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled);
+
+static inline bool scs_is_dynamic(void)
+{
+ if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
+ return false;
+ return static_branch_likely(&dynamic_scs_enabled);
+}
+
+static inline bool scs_is_enabled(void)
+{
+ if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
+ return true;
+ return scs_is_dynamic();
+}
+
#else /* CONFIG_SHADOW_CALL_STACK */
static inline void *scs_alloc(int node) { return NULL; }
@@ -62,6 +78,8 @@ static inline void scs_task_reset(struct task_struct *tsk) {}
static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
static inline void scs_release(struct task_struct *tsk) {}
static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
+static inline bool scs_is_enabled(void) { return false; }
+static inline bool scs_is_dynamic(void) { return false; }
#endif /* CONFIG_SHADOW_CALL_STACK */