bpf, arm64: sign return address for jited code

Sign return address for jited code when the kernel is built with pointer
authentication enabled.

1. Sign lr with paciasp instruction before lr is pushed to stack. Since
   paciasp acts like landing pads for function entry, no need to insert
   bti instruction before paciasp.

2. Authenticate lr with autiasp instruction after lr is poped from stack.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>

Author: Xu Kuohai

arch/arm64/net/bpf_jit.h

@@ -249,6 +249,9 @@
 /* HINTs */
 #define A64_HINT(x) aarch64_insn_gen_hint(x)
 
+#define A64_PACIASP A64_HINT(AARCH64_INSN_HINT_PACIASP)
+#define A64_AUTIASP A64_HINT(AARCH64_INSN_HINT_AUTIASP)
+
 /* BTI */
 #define A64_BTI_C  A64_HINT(AARCH64_INSN_HINT_BTIC)
 #define A64_BTI_J  A64_HINT(AARCH64_INSN_HINT_BTIJ)

arch/arm64/net/bpf_jit_comp.c

@@ -192,7 +192,7 @@ static bool is_addsub_imm(u32 imm)
 }
 
 /* Tail call offset to jump into */
-#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
+#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) || IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)
 #define PROLOGUE_OFFSET 8
 #else
 #define PROLOGUE_OFFSET 7
@@ -233,8 +233,11 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf)
 	 *
 	 */
 
+	/* Sign lr */
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL))
+		emit(A64_PACIASP, ctx);
 	/* BTI landing pad */
-	if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))
+	else if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))
 		emit(A64_BTI_C, ctx);
 
 	/* Save FP and LR registers to stay align with ARM64 AAPCS */
@@ -529,6 +532,10 @@ static void build_epilogue(struct jit_ctx *ctx)
 	/* Set return value */
 	emit(A64_MOV(1, A64_R(0), r0), ctx);
 
+	/* Authenticate lr */
+	if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL))
+		emit(A64_AUTIASP, ctx);
+
 	emit(A64_RET(A64_LR), ctx);
 }