[PATCH v1 RFC Zisslpcfi 07/20] elf: ELF header parsing in GNU property for cfi state

[Deepak Gupta]

Binaries enabled with support for control-flow integrity will have new
instructions that may fault on cpus which dont implement cfi mechanisms.
This change adds

 - stub for setting up cfi state when loading a binary. Architecture
   specific implementation can choose to implement this stub and setup
   cfi state for program.
 - define riscv ELF flag marker for forward cfi and backward cfi in
   uapi/linux/elf.h

Signed-off-by: Deepak Gupta <debug at rivosinc.com>
---
 fs/binfmt_elf.c          | 5 +++++
 include/linux/elf.h      | 8 ++++++++
 include/uapi/linux/elf.h | 6 ++++++
 3 files changed, 19 insertions(+)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 9a780fafc539..bb431052eb01 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1277,6 +1277,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
 
 	set_binfmt(&elf_format);
 
+#if defined(CONFIG_USER_SHADOW_STACK) || defined(CONFIG_USER_INDIRECT_BR_LP)
+	retval = arch_elf_setup_cfi_state(&arch_state);
+	if (retval < 0)
+		goto out;
+#endif
 #ifdef ARCH_HAS_SETUP_ADDITIONAL_PAGES
 	retval = ARCH_SETUP_ADDITIONAL_PAGES(bprm, elf_ex, !!interpreter);
 	if (retval < 0)
diff --git a/include/linux/elf.h b/include/linux/elf.h
index c9a46c4e183b..106d28f065aa 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -109,4 +109,12 @@ static inline int arch_elf_adjust_prot(int prot,
 }
 #endif
 
+#if defined(CONFIG_USER_SHADOW_STACK) || defined(CONFIG_USER_INDIRECT_BR_LP)
+extern int arch_elf_setup_cfi_state(const struct arch_elf_state *state);
+#else
+static inline int arch_elf_setup_cfi_state(const struct arch_elf_state *state)
+{
+	return 0;
+}
+#endif
 #endif /* _LINUX_ELF_H */
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 4c6a8fa5e7ed..1cbd332061dc 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -468,4 +468,10 @@ typedef struct elf64_note {
 /* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */
 #define GNU_PROPERTY_AARCH64_FEATURE_1_BTI	(1U << 0)
 
+/* .note.gnu.property types for RISCV: */
+/* Bits for GNU_PROPERTY_RISCV_FEATURE_1_FCFI/BCFI */
+#define GNU_PROPERTY_RISCV_FEATURE_1_AND  0xc0000000
+#define GNU_PROPERTY_RISCV_FEATURE_1_FCFI (1u << 0)
+#define GNU_PROPERTY_RISCV_FEATURE_1_BCFI (1u << 1)
+
 #endif /* _UAPI_LINUX_ELF_H */
-- 
2.25.1