This patch adds kernel function call support to the x86-32 bpf jit.
Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
---
arch/x86/net/bpf_jit_comp32.c | 198 ++++++++++++++++++++++++++++++++++
1 file changed, 198 insertions(+)
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index d17b67c69f89..0a7a2870f111 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -1390,6 +1390,19 @@ static inline void emit_push_r64(const u8 src[], u8 **pprog)
*pprog = prog;
}
+static void emit_push_r32(const u8 src[], u8 **pprog)
+{
+ u8 *prog = *pprog;
+ int cnt = 0;
+
+ /* mov ecx,dword ptr [ebp+off] */
+ EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_ECX), STACK_VAR(src_lo));
+ /* push ecx */
+ EMIT1(0x51);
+
+ *pprog = prog;
+}
+
static u8 get_cond_jmp_opcode(const u8 op, bool is_cmp_lo)
{
u8 jmp_cond;
@@ -1459,6 +1472,174 @@ static u8 get_cond_jmp_opcode(const u8 op, bool is_cmp_lo)
return jmp_cond;
}
+/* i386 kernel compiles with "-mregparm=3". From gcc document:
+ *
+ * ==== snippet ====
+ * regparm (number)
+ * On x86-32 targets, the regparm attribute causes the compiler
+ * to pass arguments number one to (number) if they are of integral
+ * type in registers EAX, EDX, and ECX instead of on the stack.
+ * Functions that take a variable number of arguments continue
+ * to be passed all of their arguments on the stack.
+ * ==== snippet ====
+ *
+ * The first three args of a function will be considered for
+ * putting into the 32bit register EAX, EDX, and ECX.
+ *
+ * Two 32bit registers are used to pass a 64bit arg.
+ *
+ * For example,
+ * void foo(u32 a, u32 b, u32 c, u32 d):
+ * u32 a: EAX
+ * u32 b: EDX
+ * u32 c: ECX
+ * u32 d: stack
+ *
+ * void foo(u64 a, u32 b, u32 c):
+ * u64 a: EAX (lo32) EDX (hi32)
+ * u32 b: ECX
+ * u32 c: stack
+ *
+ * void foo(u32 a, u64 b, u32 c):
+ * u32 a: EAX
+ * u64 b: EDX (lo32) ECX (hi32)
+ * u32 c: stack
+ *
+ * void foo(u32 a, u32 b, u64 c):
+ * u32 a: EAX
+ * u32 b: EDX
+ * u64 c: stack
+ *
+ * The return value will be stored in the EAX (and EDX for 64bit value).
+ *
+ * For example,
+ * u32 foo(u32 a, u32 b, u32 c):
+ * return value: EAX
+ *
+ * u64 foo(u32 a, u32 b, u32 c):
+ * return value: EAX (lo32) EDX (hi32)
+ *
+ * Notes:
+ * The verifier only accepts function having integer and pointers
+ * as its args and return value, so it does not have
+ * struct-by-value.
+ *
+ * emit_kfunc_call() finds out the btf_func_model by calling
+ * bpf_jit_find_kfunc_model(). A btf_func_model
+ * has the details about the number of args, size of each arg,
+ * and the size of the return value.
+ *
+ * It first decides how many args can be passed by EAX, EDX, and ECX.
+ * That will decide what args should be pushed to the stack:
+ * [first_stack_regno, last_stack_regno] are the bpf regnos
+ * that should be pushed to the stack.
+ *
+ * It will first push all args to the stack because the push
+ * will need to use ECX. Then, it moves
+ * [BPF_REG_1, first_stack_regno) to EAX, EDX, and ECX.
+ *
+ * When emitting a call (0xE8), it needs to figure out
+ * the jmp_offset relative to the jit-insn address immediately
+ * following the call (0xE8) instruction. At this point, it knows
+ * the end of the jit-insn address after completely translated the
+ * current (BPF_JMP | BPF_CALL) bpf-insn. It is passed as "end_addr"
+ * to the emit_kfunc_call(). Thus, it can learn the "immediate-follow-call"
+ * address by figuring out how many jit-insn is generated between
+ * the call (0xE8) and the end_addr:
+ * - 0-1 jit-insn (3 bytes each) to restore the esp pointer if there
+ * is arg pushed to the stack.
+ * - 0-2 jit-insns (3 bytes each) to handle the return value.
+ */
+static int emit_kfunc_call(const struct bpf_prog *bpf_prog, u8 *end_addr,
+ const struct bpf_insn *insn, u8 **pprog)
+{
+ const u8 arg_regs[] = { IA32_EAX, IA32_EDX, IA32_ECX };
+ int i, cnt = 0, first_stack_regno, last_stack_regno;
+ int free_arg_regs = ARRAY_SIZE(arg_regs);
+ const struct btf_func_model *fm;
+ int bytes_in_stack = 0;
+ const u8 *cur_arg_reg;
+ u8 *prog = *pprog;
+ s64 jmp_offset;
+
+ fm = bpf_jit_find_kfunc_model(bpf_prog, insn);
+ if (!fm)
+ return -EINVAL;
+
+ first_stack_regno = BPF_REG_1;
+ for (i = 0; i < fm->nr_args; i++) {
+ int regs_needed = fm->arg_size[i] > sizeof(u32) ? 2 : 1;
+
+ if (regs_needed > free_arg_regs)
+ break;
+
+ free_arg_regs -= regs_needed;
+ first_stack_regno++;
+ }
+
+ /* Push the args to the stack */
+ last_stack_regno = BPF_REG_0 + fm->nr_args;
+ for (i = last_stack_regno; i >= first_stack_regno; i--) {
+ if (fm->arg_size[i - 1] > sizeof(u32)) {
+ emit_push_r64(bpf2ia32[i], &prog);
+ bytes_in_stack += 8;
+ } else {
+ emit_push_r32(bpf2ia32[i], &prog);
+ bytes_in_stack += 4;
+ }
+ }
+
+ cur_arg_reg = &arg_regs[0];
+ for (i = BPF_REG_1; i < first_stack_regno; i++) {
+ /* mov e[adc]x,dword ptr [ebp+off] */
+ EMIT3(0x8B, add_2reg(0x40, IA32_EBP, *cur_arg_reg++),
+ STACK_VAR(bpf2ia32[i][0]));
+ if (fm->arg_size[i - 1] > sizeof(u32))
+ /* mov e[adc]x,dword ptr [ebp+off] */
+ EMIT3(0x8B, add_2reg(0x40, IA32_EBP, *cur_arg_reg++),
+ STACK_VAR(bpf2ia32[i][1]));
+ }
+
+ if (bytes_in_stack)
+ /* add esp,"bytes_in_stack" */
+ end_addr -= 3;
+
+ /* mov dword ptr [ebp+off],edx */
+ if (fm->ret_size > sizeof(u32))
+ end_addr -= 3;
+
+ /* mov dword ptr [ebp+off],eax */
+ if (fm->ret_size)
+ end_addr -= 3;
+
+ jmp_offset = (u8 *)__bpf_call_base + insn->imm - end_addr;
+ if (!is_simm32(jmp_offset)) {
+ pr_err("unsupported BPF kernel function jmp_offset:%lld\n",
+ jmp_offset);
+ return -EINVAL;
+ }
+
+ EMIT1_off32(0xE8, jmp_offset);
+
+ if (fm->ret_size)
+ /* mov dword ptr [ebp+off],eax */
+ EMIT3(0x89, add_2reg(0x40, IA32_EBP, IA32_EAX),
+ STACK_VAR(bpf2ia32[BPF_REG_0][0]));
+
+ if (fm->ret_size > sizeof(u32))
+ /* mov dword ptr [ebp+off],edx */
+ EMIT3(0x89, add_2reg(0x40, IA32_EBP, IA32_EDX),
+ STACK_VAR(bpf2ia32[BPF_REG_0][1]));
+
+ if (bytes_in_stack)
+ /* add esp,"bytes_in_stack" */
+ EMIT3(0x83, add_1reg(0xC0, IA32_ESP), bytes_in_stack);
+
+ *pprog = prog;
+
+ return 0;
+}
+
static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
int oldproglen, struct jit_context *ctx)
{
@@ -1888,6 +2069,18 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
if (insn->src_reg == BPF_PSEUDO_CALL)
goto notyet;
+ if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+ int err;
+
+ err = emit_kfunc_call(bpf_prog,
+ image + addrs[i],
+ insn, &prog);
+
+ if (err)
+ return err;
+ break;
+ }
+
func = (u8 *) __bpf_call_base + imm32;
jmp_offset = func - (image + addrs[i]);
@@ -2393,3 +2586,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
tmp : orig_prog);
return prog;
}
+
+bool bpf_jit_supports_kfunc_call(void)
+{
+ return true;
+}
--
2.30.2
