elf: Allow arch to tweak initial mmap prot flags

An arch may want to tweak the mmap prot flags for an
ELFexecutable's initial mappings.  For example, arm64 is going to
need to add PROT_BTI for executable pages in an ELF process whose
executable is marked as using Branch Target Identification (an
ARMv8.5-A control flow integrity feature).

So that this can be done in a generic way, add a hook
arch_elf_adjust_prot() to modify the prot flags as desired: arches
can select CONFIG_HAVE_ELF_PROT and implement their own backend
where necessary.

By default, leave the prot flags unchanged.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/elf.h b/include/linux/elf.h
index db5113479f5e..5d5b0321da0b 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -87,4 +87,16 @@ extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
 				   bool compat, struct arch_elf_state *arch);
 #endif
 
+#ifdef CONFIG_ARCH_HAVE_ELF_PROT
+int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
+			 bool has_interp, bool is_interp);
+#else
+static inline int arch_elf_adjust_prot(int prot,
+				       const struct arch_elf_state *state,
+				       bool has_interp, bool is_interp)
+{
+	return prot;
+}
+#endif
+
 #endif /* _LINUX_ELF_H */