arm64/cfi,bpf: Support kCFI + BPF on arm64

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 <[email protected]>
Co-developed-by: Maxwell Bland <[email protected]>
Signed-off-by: Maxwell Bland <[email protected]>
Co-developed-by: Sami Tolvanen <[email protected]>
Signed-off-by: Sami Tolvanen <[email protected]>
Tested-by: Dao Huang <[email protected]>

Author: puranjaymohan

arch/arm64/include/asm/cfi.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARM64_CFI_H
+#define _ASM_ARM64_CFI_H
+
+#ifdef CONFIG_CFI_CLANG
+#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
+#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_ARM64_CFI_H */

arch/arm64/kernel/alternative.c

@@ -8,11 +8,13 @@
 
 #define pr_fmt(fmt) "alternatives: " fmt
 
+#include <linux/cfi_types.h>
 #include <linux/init.h>
 #include <linux/cpu.h>
 #include <linux/elf.h>
 #include <asm/cacheflush.h>
 #include <asm/alternative.h>
+#include <asm/cfi.h>
 #include <asm/cpufeature.h>
 #include <asm/insn.h>
 #include <asm/module.h>
@@ -298,3 +300,26 @@ noinstr void alt_cb_patch_nops(struct alt_instr *alt, __le32 *origptr,
 		updptr[i] = cpu_to_le32(aarch64_insn_gen_nop());
 }
 EXPORT_SYMBOL(alt_cb_patch_nops);
+
+#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 /* CONFIG_CFI_CLANG */

arch/arm64/net/bpf_jit_comp.c

@@ -9,6 +9,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/bpf.h>
+#include <linux/cfi.h>
 #include <linux/filter.h>
 #include <linux/memory.h>
 #include <linux/printk.h>
@@ -164,6 +165,12 @@ 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
@@ -474,7 +481,6 @@ 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;
 
 	/*
@@ -500,6 +506,9 @@ 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
@@ -2009,9 +2018,9 @@ 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;
@@ -2271,6 +2280,12 @@ 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
@@ -2790,6 +2805,7 @@ 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));