[PATCH bpf-next v10 0/3] Support kCFI + BPF on arm64

[PATCH bpf-next v10 0/3] Support kCFI + BPF on arm64

[Sami Tolvanen]

Hi folks,

These patches add KCFI types to arm64 BPF JIT output. Puranjay and
Maxwell have been working on this for some time now, but I haven't
seen any progress since June 2024, so I decided to pick up the latest
version[1] posted by Maxwell and fix the few remaining issues I
noticed. I confirmed that with these patches applied, I no longer see
CFI failures in jitted code when running BPF self-tests on arm64.

[1] https://lore.kernel.org/linux-arm-kernel/ptrugmna4xb5o5lo4xislf4rlz7avdmd4pfho5fjwtjj7v422u@iqrwfrbwuxrq/

Note that in order to enable CFI for jitted code, we need to define
__bpfcall in a file included by include/linux/bpf.h. In v10, I'm still
adding an include/asm/cfi.h header file for consistency with other
architectures, even though the file no longer contains anything else.
If you'd prefer to move this to another header file, I'm certainly
open to suggestions.

Sami

---
v10:
- Rebased to bpf-next/master again.
- Added a patch to moved duplicate type hash variables and helper
  functions to common CFI code.

v9: https://lore.kernel.org/bpf/20250505223437.3722164-4-samitolvanen@google.com/
- Rebased to bpf-next/master to fix merge x86 merge conflicts.
- Fixed checkpatch warnings about Co-developed-by tags and including
  <asm/cfi.h>.
- Picked up Tested-by tags.

v8: https://lore.kernel.org/bpf/20250310222942.1988975-4-samitolvanen@google.com/
- Changed DEFINE_CFI_TYPE to use .4byte to match __CFI_TYPE.
- Changed cfi_get_func_hash() to again use get_kernel_nofault().
- Fixed a panic in bpf_jit_free() by resetting prog->bpf_func before
  calling bpf_jit_binary_pack_hdr().

---
Mark Rutland (1):
  cfi: add C CFI type macro

Puranjay Mohan (1):
  arm64/cfi,bpf: Support kCFI + BPF on arm64

Sami Tolvanen (1):
  cfi: Move BPF CFI types and helpers to generic code

 arch/arm64/include/asm/cfi.h  |  7 +++++
 arch/arm64/net/bpf_jit_comp.c | 22 +++++++++++++--
 arch/riscv/include/asm/cfi.h  | 16 -----------
 arch/riscv/kernel/cfi.c       | 53 -----------------------------------
 arch/x86/include/asm/cfi.h    |  9 ------
 arch/x86/kernel/alternative.c | 37 ------------------------
 include/linux/cfi.h           | 37 ++++++++++++++++++------
 include/linux/cfi_types.h     | 23 +++++++++++++++
 kernel/cfi.c                  | 25 +++++++++++++++++
 9 files changed, 103 insertions(+), 126 deletions(-)
 create mode 100644 arch/arm64/include/asm/cfi.h


base-commit: e860a98c8aebd8de82c0ee901acf5a759acd4570
-- 
2.50.0.727.gbf7dc18ff4-goog

[PATCH bpf-next v10 1/3] cfi: add C CFI type macro

[Sami Tolvanen]

From: Mark Rutland <mark.rutland@arm.com>

Currently x86 and riscv open-code 4 instances of the same logic to
define a u32 variable with the KCFI typeid of a given function.

Replace the duplicate logic with a common macro.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Co-developed-by: Maxwell Bland <mbland@motorola.com>
Signed-off-by: Maxwell Bland <mbland@motorola.com>
Co-developed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Dao Huang <huangdao1@oppo.com>
---
 arch/riscv/kernel/cfi.c       | 35 +++--------------------------------
 arch/x86/kernel/alternative.c | 31 +++----------------------------
 include/linux/cfi_types.h     | 23 +++++++++++++++++++++++
 3 files changed, 29 insertions(+), 60 deletions(-)

diff --git a/arch/riscv/kernel/cfi.c b/arch/riscv/kernel/cfi.c
index 64bdd3e1ab8c..e7aec5f36dd5 100644
--- a/arch/riscv/kernel/cfi.c
+++ b/arch/riscv/kernel/cfi.c
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2023 Google LLC
  */
+#include <linux/cfi_types.h>
 #include <linux/cfi.h>
 #include <asm/insn.h>
 
@@ -82,41 +83,11 @@ struct bpf_insn;
 /* Must match bpf_func_t / DEFINE_BPF_PROG_RUN() */
 extern unsigned int __bpf_prog_runX(const void *ctx,
 				    const struct bpf_insn *insn);
-
-/*
- * Force a reference to the external symbol so the compiler generates
- * __kcfi_typid.
- */
-__ADDRESSABLE(__bpf_prog_runX);
-
-/* u32 __ro_after_init cfi_bpf_hash = __kcfi_typeid___bpf_prog_runX; */
-asm (
-"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"
-"	.type	cfi_bpf_hash,@object				\n"
-"	.globl	cfi_bpf_hash					\n"
-"	.p2align	2, 0x0					\n"
-"cfi_bpf_hash:							\n"
-"	.word	__kcfi_typeid___bpf_prog_runX			\n"
-"	.size	cfi_bpf_hash, 4					\n"
-"	.popsection						\n"
-);
+DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
 
 /* Must match bpf_callback_t */
 extern u64 __bpf_callback_fn(u64, u64, u64, u64, u64);
-
-__ADDRESSABLE(__bpf_callback_fn);
-
-/* u32 __ro_after_init cfi_bpf_subprog_hash = __kcfi_typeid___bpf_callback_fn; */
-asm (
-"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"
-"	.type	cfi_bpf_subprog_hash,@object			\n"
-"	.globl	cfi_bpf_subprog_hash				\n"
-"	.p2align	2, 0x0					\n"
-"cfi_bpf_subprog_hash:						\n"
-"	.word	__kcfi_typeid___bpf_callback_fn			\n"
-"	.size	cfi_bpf_subprog_hash, 4				\n"
-"	.popsection						\n"
-);
+DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
 
 u32 cfi_get_func_hash(void *func)
 {
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ea1d984166cd..a555665b4d9c 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2,6 +2,7 @@
 #define pr_fmt(fmt) "SMP alternatives: " fmt
 
 #include <linux/mmu_context.h>
+#include <linux/cfi_types.h>
 #include <linux/perf_event.h>
 #include <linux/vmalloc.h>
 #include <linux/memory.h>
@@ -1189,37 +1190,11 @@ struct bpf_insn;
 /* Must match bpf_func_t / DEFINE_BPF_PROG_RUN() */
 extern unsigned int __bpf_prog_runX(const void *ctx,
 				    const struct bpf_insn *insn);
-
-KCFI_REFERENCE(__bpf_prog_runX);
-
-/* u32 __ro_after_init cfi_bpf_hash = __kcfi_typeid___bpf_prog_runX; */
-asm (
-"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"
-"	.type	cfi_bpf_hash,@object				\n"
-"	.globl	cfi_bpf_hash					\n"
-"	.p2align	2, 0x0					\n"
-"cfi_bpf_hash:							\n"
-"	.long	__kcfi_typeid___bpf_prog_runX			\n"
-"	.size	cfi_bpf_hash, 4					\n"
-"	.popsection						\n"
-);
+DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
 
 /* Must match bpf_callback_t */
 extern u64 __bpf_callback_fn(u64, u64, u64, u64, u64);
-
-KCFI_REFERENCE(__bpf_callback_fn);
-
-/* u32 __ro_after_init cfi_bpf_subprog_hash = __kcfi_typeid___bpf_callback_fn; */
-asm (
-"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"
-"	.type	cfi_bpf_subprog_hash,@object			\n"
-"	.globl	cfi_bpf_subprog_hash				\n"
-"	.p2align	2, 0x0					\n"
-"cfi_bpf_subprog_hash:						\n"
-"	.long	__kcfi_typeid___bpf_callback_fn			\n"
-"	.size	cfi_bpf_subprog_hash, 4				\n"
-"	.popsection						\n"
-);
+DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
 
 u32 cfi_get_func_hash(void *func)
 {
diff --git a/include/linux/cfi_types.h b/include/linux/cfi_types.h
index 6b8713675765..e5567c0fd0b3 100644
--- a/include/linux/cfi_types.h
+++ b/include/linux/cfi_types.h
@@ -41,5 +41,28 @@
 	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)
 #endif
 
+#else /* __ASSEMBLY__ */
+
+#ifdef CONFIG_CFI_CLANG
+#define DEFINE_CFI_TYPE(name, func)						\
+	/*									\
+	 * Force a reference to the function so the compiler generates		\
+	 * __kcfi_typeid_<func>.						\
+	 */									\
+	__ADDRESSABLE(func);							\
+	/* u32 name __ro_after_init = __kcfi_typeid_<func> */			\
+	extern u32 name;							\
+	asm (									\
+	"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"	\
+	"	.type	" #name ",@object				\n"	\
+	"	.globl	" #name "					\n"	\
+	"	.p2align	2, 0x0					\n"	\
+	#name ":							\n"	\
+	"	.4byte	__kcfi_typeid_" #func "				\n"	\
+	"	.size	" #name ", 4					\n"	\
+	"	.popsection						\n"	\
+	);
+#endif
+
 #endif /* __ASSEMBLY__ */
 #endif /* _LINUX_CFI_TYPES_H */
-- 
2.50.0.727.gbf7dc18ff4-goog

Re: [PATCH bpf-next v10 1/3] cfi: add C CFI type macro

[Will Deacon]

On Tue, Jul 15, 2025 at 10:57:35PM +0000, Sami Tolvanen wrote:
> From: Mark Rutland <mark.rutland@arm.com>
> 
> Currently x86 and riscv open-code 4 instances of the same logic to
> define a u32 variable with the KCFI typeid of a given function.
> 
> Replace the duplicate logic with a common macro.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Co-developed-by: Maxwell Bland <mbland@motorola.com>
> Signed-off-by: Maxwell Bland <mbland@motorola.com>
> Co-developed-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Tested-by: Dao Huang <huangdao1@oppo.com>
> ---
>  arch/riscv/kernel/cfi.c       | 35 +++--------------------------------
>  arch/x86/kernel/alternative.c | 31 +++----------------------------
>  include/linux/cfi_types.h     | 23 +++++++++++++++++++++++
>  3 files changed, 29 insertions(+), 60 deletions(-)

[...]

> diff --git a/include/linux/cfi_types.h b/include/linux/cfi_types.h
> index 6b8713675765..e5567c0fd0b3 100644
> --- a/include/linux/cfi_types.h
> +++ b/include/linux/cfi_types.h
> @@ -41,5 +41,28 @@
>  	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)
>  #endif
>  
> +#else /* __ASSEMBLY__ */
> +
> +#ifdef CONFIG_CFI_CLANG
> +#define DEFINE_CFI_TYPE(name, func)						\
> +	/*									\
> +	 * Force a reference to the function so the compiler generates		\
> +	 * __kcfi_typeid_<func>.						\
> +	 */									\
> +	__ADDRESSABLE(func);							\
> +	/* u32 name __ro_after_init = __kcfi_typeid_<func> */			\
> +	extern u32 name;							\
> +	asm (									\
> +	"	.pushsection	.data..ro_after_init,\"aw\",@progbits	\n"	\
> +	"	.type	" #name ",@object				\n"	\
> +	"	.globl	" #name "					\n"	\
> +	"	.p2align	2, 0x0					\n"	\
> +	#name ":							\n"	\
> +	"	.4byte	__kcfi_typeid_" #func "				\n"	\
> +	"	.size	" #name ", 4					\n"	\
> +	"	.popsection						\n"	\
> +	);
> +#endif

This looks good to me. I was initially a bit worried about the portability
of the '.4byte' directive, but it seems that cfi_types.h is already using
that for the __CFI_TYPE() macro so I'm assuming it's not an issue.

In which case:

Acked-by: Will Deacon <will@kernel.org>

Thanks for cleaning it up.

Will

[PATCH bpf-next v10 2/3] cfi: Move BPF CFI types and helpers to generic code

[Sami Tolvanen]

Instead of duplicating the same code for each architecture, move
the CFI type hash variables for BPF function types and related
helper functions to generic CFI code, and allow architectures to
override the function definitions if needed.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/riscv/include/asm/cfi.h  | 16 ---------------
 arch/riscv/kernel/cfi.c       | 24 -----------------------
 arch/x86/include/asm/cfi.h    |  9 ---------
 arch/x86/kernel/alternative.c | 12 ------------
 include/linux/cfi.h           | 37 +++++++++++++++++++++++++++--------
 kernel/cfi.c                  | 25 +++++++++++++++++++++++
 6 files changed, 54 insertions(+), 69 deletions(-)

diff --git a/arch/riscv/include/asm/cfi.h b/arch/riscv/include/asm/cfi.h
index fb9696d7a3f2..4508aaa7a2fd 100644
--- a/arch/riscv/include/asm/cfi.h
+++ b/arch/riscv/include/asm/cfi.h
@@ -14,27 +14,11 @@ struct pt_regs;
 #ifdef CONFIG_CFI_CLANG
 enum bug_trap_type handle_cfi_failure(struct pt_regs *regs);
 #define __bpfcall
-static inline int cfi_get_offset(void)
-{
-	return 4;
-}
-
-#define cfi_get_offset cfi_get_offset
-extern u32 cfi_bpf_hash;
-extern u32 cfi_bpf_subprog_hash;
-extern u32 cfi_get_func_hash(void *func);
 #else
 static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
 {
 	return BUG_TRAP_TYPE_NONE;
 }
-
-#define cfi_bpf_hash 0U
-#define cfi_bpf_subprog_hash 0U
-static inline u32 cfi_get_func_hash(void *func)
-{
-	return 0;
-}
 #endif /* CONFIG_CFI_CLANG */
 
 #endif /* _ASM_RISCV_CFI_H */
diff --git a/arch/riscv/kernel/cfi.c b/arch/riscv/kernel/cfi.c
index e7aec5f36dd5..6ec9dbd7292e 100644
--- a/arch/riscv/kernel/cfi.c
+++ b/arch/riscv/kernel/cfi.c
@@ -4,7 +4,6 @@
  *
  * Copyright (C) 2023 Google LLC
  */
-#include <linux/cfi_types.h>
 #include <linux/cfi.h>
 #include <asm/insn.h>
 
@@ -76,26 +75,3 @@ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
 
 	return report_cfi_failure(regs, regs->epc, &target, type);
 }
-
-#ifdef CONFIG_CFI_CLANG
-struct bpf_insn;
-
-/* Must match bpf_func_t / DEFINE_BPF_PROG_RUN() */
-extern unsigned int __bpf_prog_runX(const void *ctx,
-				    const struct bpf_insn *insn);
-DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
-
-/* Must match bpf_callback_t */
-extern u64 __bpf_callback_fn(u64, u64, u64, u64, u64);
-DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
-
-u32 cfi_get_func_hash(void *func)
-{
-	u32 hash;
-
-	if (get_kernel_nofault(hash, func - cfi_get_offset()))
-		return 0;
-
-	return hash;
-}
-#endif
diff --git a/arch/x86/include/asm/cfi.h b/arch/x86/include/asm/cfi.h
index 3e51ba459154..64506a91971b 100644
--- a/arch/x86/include/asm/cfi.h
+++ b/arch/x86/include/asm/cfi.h
@@ -116,8 +116,6 @@ struct pt_regs;
 #ifdef CONFIG_CFI_CLANG
 enum bug_trap_type handle_cfi_failure(struct pt_regs *regs);
 #define __bpfcall
-extern u32 cfi_bpf_hash;
-extern u32 cfi_bpf_subprog_hash;
 
 static inline int cfi_get_offset(void)
 {
@@ -134,7 +132,6 @@ static inline int cfi_get_offset(void)
 }
 #define cfi_get_offset cfi_get_offset
 
-extern u32 cfi_get_func_hash(void *func);
 extern int cfi_get_func_arity(void *func);
 
 #ifdef CONFIG_FINEIBT
@@ -153,12 +150,6 @@ static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
 {
 	return BUG_TRAP_TYPE_NONE;
 }
-#define cfi_bpf_hash 0U
-#define cfi_bpf_subprog_hash 0U
-static inline u32 cfi_get_func_hash(void *func)
-{
-	return 0;
-}
 static inline int cfi_get_func_arity(void *func)
 {
 	return 0;
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a555665b4d9c..9f6b7dab2d9a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2,7 +2,6 @@
 #define pr_fmt(fmt) "SMP alternatives: " fmt
 
 #include <linux/mmu_context.h>
-#include <linux/cfi_types.h>
 #include <linux/perf_event.h>
 #include <linux/vmalloc.h>
 #include <linux/memory.h>
@@ -1185,17 +1184,6 @@ bool cfi_bhi __ro_after_init = false;
 #endif
 
 #ifdef CONFIG_CFI_CLANG
-struct bpf_insn;
-
-/* Must match bpf_func_t / DEFINE_BPF_PROG_RUN() */
-extern unsigned int __bpf_prog_runX(const void *ctx,
-				    const struct bpf_insn *insn);
-DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
-
-/* Must match bpf_callback_t */
-extern u64 __bpf_callback_fn(u64, u64, u64, u64, u64);
-DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
-
 u32 cfi_get_func_hash(void *func)
 {
 	u32 hash;
diff --git a/include/linux/cfi.h b/include/linux/cfi.h
index 1db17ecbb86c..53ed07cb9258 100644
--- a/include/linux/cfi.h
+++ b/include/linux/cfi.h
@@ -11,16 +11,9 @@
 #include <linux/module.h>
 #include <asm/cfi.h>
 
+#ifdef CONFIG_CFI_CLANG
 extern bool cfi_warn;
 
-#ifndef cfi_get_offset
-static inline int cfi_get_offset(void)
-{
-	return 0;
-}
-#endif
-
-#ifdef CONFIG_CFI_CLANG
 enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
 				      unsigned long *target, u32 type);
 
@@ -29,6 +22,34 @@ static inline enum bug_trap_type report_cfi_failure_noaddr(struct pt_regs *regs,
 {
 	return report_cfi_failure(regs, addr, NULL, 0);
 }
+
+#ifndef cfi_get_offset
+/*
+ * Returns the CFI prefix offset. By default, the compiler emits only
+ * a 4-byte CFI type hash before the function. If an architecture
+ * uses -fpatchable-function-entry=N,M where M>0 to change the prefix
+ * offset, they must override this function.
+ */
+static inline int cfi_get_offset(void)
+{
+	return 4;
+}
+#endif
+
+u32 cfi_get_func_hash(void *func);
+
+/* CFI type hashes for BPF function types */
+extern u32 cfi_bpf_hash;
+extern u32 cfi_bpf_subprog_hash;
+
+#else /* CONFIG_CFI_CLANG */
+
+static inline int cfi_get_offset(void) { return 0; }
+static inline u32 cfi_get_func_hash(void *func) { return 0; }
+
+#define cfi_bpf_hash 0U
+#define cfi_bpf_subprog_hash 0U
+
 #endif /* CONFIG_CFI_CLANG */
 
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
diff --git a/kernel/cfi.c b/kernel/cfi.c
index 422fa4f958ae..68b3760c15a6 100644
--- a/kernel/cfi.c
+++ b/kernel/cfi.c
@@ -5,6 +5,8 @@
  * Copyright (C) 2022 Google LLC
  */
 
+#include <linux/bpf.h>
+#include <linux/cfi_types.h>
 #include <linux/cfi.h>
 
 bool cfi_warn __ro_after_init = IS_ENABLED(CONFIG_CFI_PERMISSIVE);
@@ -27,6 +29,29 @@ enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
 	return BUG_TRAP_TYPE_BUG;
 }
 
+u32 __weak cfi_get_func_hash(void *func)
+{
+	u32 hash;
+
+	if (get_kernel_nofault(hash, func - cfi_get_offset()))
+		return 0;
+
+	return hash;
+}
+
+/*
+ * Declare two non-existent functions with types that match bpf_func_t and
+ * bpf_callback_t pointers, and use DEFINE_CFI_TYPE to define type hash
+ * variables for each function type. The cfi_bpf_* variables are used by
+ * arch-specific BPF JIT implementations to ensure indirectly callable JIT
+ * code has matching CFI type hashes.
+ */
+typeof(*(bpf_func_t)0) __bpf_prog_runX;
+DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
+
+typeof(*(bpf_callback_t)0) __bpf_callback_fn;
+DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
+
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
 static inline unsigned long trap_address(s32 *p)
 {
-- 
2.50.0.727.gbf7dc18ff4-goog

Re: [PATCH bpf-next v10 2/3] cfi: Move BPF CFI types and helpers to generic code

[Will Deacon]

On Tue, Jul 15, 2025 at 10:57:36PM +0000, Sami Tolvanen wrote:
> Instead of duplicating the same code for each architecture, move
> the CFI type hash variables for BPF function types and related
> helper functions to generic CFI code, and allow architectures to
> override the function definitions if needed.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  arch/riscv/include/asm/cfi.h  | 16 ---------------
>  arch/riscv/kernel/cfi.c       | 24 -----------------------
>  arch/x86/include/asm/cfi.h    |  9 ---------
>  arch/x86/kernel/alternative.c | 12 ------------
>  include/linux/cfi.h           | 37 +++++++++++++++++++++++++++--------
>  kernel/cfi.c                  | 25 +++++++++++++++++++++++
>  6 files changed, 54 insertions(+), 69 deletions(-)

[...]

> @@ -27,6 +29,29 @@ enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
>  	return BUG_TRAP_TYPE_BUG;
>  }
>  
> +u32 __weak cfi_get_func_hash(void *func)
> +{
> +	u32 hash;
> +
> +	if (get_kernel_nofault(hash, func - cfi_get_offset()))
> +		return 0;
> +
> +	return hash;
> +}

Do you really need the '__weak' function definition here, or could you
use an '#ifndef cfi_get_func_hash' guard, a bit like you're doing for
cfi_get_offset()?

Will

Re: [PATCH bpf-next v10 2/3] cfi: Move BPF CFI types and helpers to generic code

[Sami Tolvanen]

On Fri, Jul 18, 2025 at 4:40 AM Will Deacon <will@kernel.org> wrote:
>
> On Tue, Jul 15, 2025 at 10:57:36PM +0000, Sami Tolvanen wrote:
> >
> > +u32 __weak cfi_get_func_hash(void *func)
> > +{
> > +     u32 hash;
> > +
> > +     if (get_kernel_nofault(hash, func - cfi_get_offset()))
> > +             return 0;
> > +
> > +     return hash;
> > +}
>
> Do you really need the '__weak' function definition here, or could you
> use an '#ifndef cfi_get_func_hash' guard, a bit like you're doing for
> cfi_get_offset()?

Good point, it's not really necessary. I'll move this behind a guard instead.

Sami

[PATCH bpf-next v10 3/3] arm64/cfi,bpf: Support kCFI + BPF on arm64

[Sami Tolvanen]

From: Puranjay Mohan <puranjay12@gmail.com>

Currently, bpf_dispatcher_*_func() is marked with `__nocfi` therefore
calling BPF programs from this interface doesn't cause CFI warnings.

When BPF programs are called directly from C: from BPF helpers or
struct_ops, CFI warnings are generated.

Implement proper CFI prologues for the BPF programs and callbacks and
drop __nocfi for arm64. Fix the trampoline generation code to emit kCFI
prologue when a struct_ops trampoline is being prepared.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Co-developed-by: Maxwell Bland <mbland@motorola.com>
Signed-off-by: Maxwell Bland <mbland@motorola.com>
Co-developed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Dao Huang <huangdao1@oppo.com>
---
 arch/arm64/include/asm/cfi.h  |  7 +++++++
 arch/arm64/net/bpf_jit_comp.c | 22 +++++++++++++++++++---
 2 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/cfi.h

diff --git a/arch/arm64/include/asm/cfi.h b/arch/arm64/include/asm/cfi.h
new file mode 100644
index 000000000000..ab90f0351b7a
--- /dev/null
+++ b/arch/arm64/include/asm/cfi.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARM64_CFI_H
+#define _ASM_ARM64_CFI_H
+
+#define __bpfcall
+
+#endif /* _ASM_ARM64_CFI_H */
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index b6c42b5c9668..7509ac6e76bf 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -10,6 +10,7 @@
 #include <linux/arm-smccc.h>
 #include <linux/bitfield.h>
 #include <linux/bpf.h>
+#include <linux/cfi.h>
 #include <linux/filter.h>
 #include <linux/memory.h>
 #include <linux/printk.h>
@@ -166,6 +167,12 @@ static inline void emit_bti(u32 insn, struct jit_ctx *ctx)
 		emit(insn, ctx);
 }
 
+static inline void emit_kcfi(u32 hash, struct jit_ctx *ctx)
+{
+	if (IS_ENABLED(CONFIG_CFI_CLANG))
+		emit(hash, ctx);
+}
+
 /*
  * Kernel addresses in the vmalloc space use at most 48 bits, and the
  * remaining bits are guaranteed to be 0x1. So we can compose the address
@@ -476,7 +483,6 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf)
 	const bool is_main_prog = !bpf_is_subprog(prog);
 	const u8 fp = bpf2a64[BPF_REG_FP];
 	const u8 arena_vm_base = bpf2a64[ARENA_VM_START];
-	const int idx0 = ctx->idx;
 	int cur_offset;
 
 	/*
@@ -502,6 +508,9 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf)
 	 *
 	 */
 
+	emit_kcfi(is_main_prog ? cfi_bpf_hash : cfi_bpf_subprog_hash, ctx);
+	const int idx0 = ctx->idx;
+
 	/* bpf function may be invoked by 3 instruction types:
 	 * 1. bl, attached via freplace to bpf prog via short jump
 	 * 2. br, attached via freplace to bpf prog via long jump
@@ -2055,9 +2064,9 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 		jit_data->ro_header = ro_header;
 	}
 
-	prog->bpf_func = (void *)ctx.ro_image;
+	prog->bpf_func = (void *)ctx.ro_image + cfi_get_offset();
 	prog->jited = 1;
-	prog->jited_len = prog_size;
+	prog->jited_len = prog_size - cfi_get_offset();
 
 	if (!prog->is_func || extra_pass) {
 		int i;
@@ -2431,6 +2440,12 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
 	/* return address locates above FP */
 	retaddr_off = stack_size + 8;
 
+	if (flags & BPF_TRAMP_F_INDIRECT) {
+		/*
+		 * Indirect call for bpf_struct_ops
+		 */
+		emit_kcfi(cfi_get_func_hash(func_addr), ctx);
+	}
 	/* bpf trampoline may be invoked by 3 instruction types:
 	 * 1. bl, attached to bpf prog or kernel function via short jump
 	 * 2. br, attached to bpf prog or kernel function via long jump
@@ -2947,6 +2962,7 @@ void bpf_jit_free(struct bpf_prog *prog)
 					   sizeof(jit_data->header->size));
 			kfree(jit_data);
 		}
+		prog->bpf_func -= cfi_get_offset();
 		hdr = bpf_jit_binary_pack_hdr(prog);
 		bpf_jit_binary_pack_free(hdr, NULL);
 		WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(prog));
-- 
2.50.0.727.gbf7dc18ff4-goog

Re: [PATCH bpf-next v10 3/3] arm64/cfi,bpf: Support kCFI + BPF on arm64

[Will Deacon]

On Tue, Jul 15, 2025 at 10:57:37PM +0000, Sami Tolvanen wrote:
> From: Puranjay Mohan <puranjay12@gmail.com>
> 
> Currently, bpf_dispatcher_*_func() is marked with `__nocfi` therefore
> calling BPF programs from this interface doesn't cause CFI warnings.
> 
> When BPF programs are called directly from C: from BPF helpers or
> struct_ops, CFI warnings are generated.
> 
> Implement proper CFI prologues for the BPF programs and callbacks and
> drop __nocfi for arm64. Fix the trampoline generation code to emit kCFI
> prologue when a struct_ops trampoline is being prepared.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> Co-developed-by: Maxwell Bland <mbland@motorola.com>
> Signed-off-by: Maxwell Bland <mbland@motorola.com>
> Co-developed-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Tested-by: Dao Huang <huangdao1@oppo.com>
> ---
>  arch/arm64/include/asm/cfi.h  |  7 +++++++
>  arch/arm64/net/bpf_jit_comp.c | 22 +++++++++++++++++++---
>  2 files changed, 26 insertions(+), 3 deletions(-)
>  create mode 100644 arch/arm64/include/asm/cfi.h

> diff --git a/arch/arm64/include/asm/cfi.h b/arch/arm64/include/asm/cfi.h
> new file mode 100644
> index 000000000000..ab90f0351b7a
> --- /dev/null
> +++ b/arch/arm64/include/asm/cfi.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_ARM64_CFI_H
> +#define _ASM_ARM64_CFI_H
> +
> +#define __bpfcall
> +
> +#endif /* _ASM_ARM64_CFI_H */

So close to not needing the arch header at all!

Acked-by: Will Deacon <will@kernel.org>

Will