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Diffstat (limited to 'arch/x86/net/bpf_jit_comp.c')
-rw-r--r--arch/x86/net/bpf_jit_comp.c161
1 files changed, 131 insertions, 30 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d25d81c8ecc0..06b080b61aa5 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -64,6 +64,56 @@ static bool is_imm8(int value)
return value <= 127 && value >= -128;
}
+/*
+ * Let us limit the positive offset to be <= 123.
+ * This is to ensure eventual jit convergence For the following patterns:
+ * ...
+ * pass4, final_proglen=4391:
+ * ...
+ * 20e: 48 85 ff test rdi,rdi
+ * 211: 74 7d je 0x290
+ * 213: 48 8b 77 00 mov rsi,QWORD PTR [rdi+0x0]
+ * ...
+ * 289: 48 85 ff test rdi,rdi
+ * 28c: 74 17 je 0x2a5
+ * 28e: e9 7f ff ff ff jmp 0x212
+ * 293: bf 03 00 00 00 mov edi,0x3
+ * Note that insn at 0x211 is 2-byte cond jump insn for offset 0x7d (-125)
+ * and insn at 0x28e is 5-byte jmp insn with offset -129.
+ *
+ * pass5, final_proglen=4392:
+ * ...
+ * 20e: 48 85 ff test rdi,rdi
+ * 211: 0f 84 80 00 00 00 je 0x297
+ * 217: 48 8b 77 00 mov rsi,QWORD PTR [rdi+0x0]
+ * ...
+ * 28d: 48 85 ff test rdi,rdi
+ * 290: 74 1a je 0x2ac
+ * 292: eb 84 jmp 0x218
+ * 294: bf 03 00 00 00 mov edi,0x3
+ * Note that insn at 0x211 is 6-byte cond jump insn now since its offset
+ * becomes 0x80 based on previous round (0x293 - 0x213 = 0x80).
+ * At the same time, insn at 0x292 is a 2-byte insn since its offset is
+ * -124.
+ *
+ * pass6 will repeat the same code as in pass4 and this will prevent
+ * eventual convergence.
+ *
+ * To fix this issue, we need to break je (2->6 bytes) <-> jmp (5->2 bytes)
+ * cycle in the above. In the above example je offset <= 0x7c should work.
+ *
+ * For other cases, je <-> je needs offset <= 0x7b to avoid no convergence
+ * issue. For jmp <-> je and jmp <-> jmp cases, jmp offset <= 0x7c should
+ * avoid no convergence issue.
+ *
+ * Overall, let us limit the positive offset for 8bit cond/uncond jmp insn
+ * to maximum 123 (0x7b). This way, the jit pass can eventually converge.
+ */
+static bool is_imm8_jmp_offset(int value)
+{
+ return value <= 123 && value >= -128;
+}
+
static bool is_simm32(s64 value)
{
return value == (s64)(s32)value;
@@ -273,7 +323,7 @@ struct jit_context {
/* Number of bytes emit_patch() needs to generate instructions */
#define X86_PATCH_SIZE 5
/* Number of bytes that will be skipped on tailcall */
-#define X86_TAIL_CALL_OFFSET (11 + ENDBR_INSN_SIZE)
+#define X86_TAIL_CALL_OFFSET (12 + ENDBR_INSN_SIZE)
static void push_r12(u8 **pprog)
{
@@ -403,6 +453,37 @@ static void emit_cfi(u8 **pprog, u32 hash)
*pprog = prog;
}
+static void emit_prologue_tail_call(u8 **pprog, bool is_subprog)
+{
+ u8 *prog = *pprog;
+
+ if (!is_subprog) {
+ /* cmp rax, MAX_TAIL_CALL_CNT */
+ EMIT4(0x48, 0x83, 0xF8, MAX_TAIL_CALL_CNT);
+ EMIT2(X86_JA, 6); /* ja 6 */
+ /* rax is tail_call_cnt if <= MAX_TAIL_CALL_CNT.
+ * case1: entry of main prog.
+ * case2: tail callee of main prog.
+ */
+ EMIT1(0x50); /* push rax */
+ /* Make rax as tail_call_cnt_ptr. */
+ EMIT3(0x48, 0x89, 0xE0); /* mov rax, rsp */
+ EMIT2(0xEB, 1); /* jmp 1 */
+ /* rax is tail_call_cnt_ptr if > MAX_TAIL_CALL_CNT.
+ * case: tail callee of subprog.
+ */
+ EMIT1(0x50); /* push rax */
+ /* push tail_call_cnt_ptr */
+ EMIT1(0x50); /* push rax */
+ } else { /* is_subprog */
+ /* rax is tail_call_cnt_ptr. */
+ EMIT1(0x50); /* push rax */
+ EMIT1(0x50); /* push rax */
+ }
+
+ *pprog = prog;
+}
+
/*
* Emit x86-64 prologue code for BPF program.
* bpf_tail_call helper will skip the first X86_TAIL_CALL_OFFSET bytes
@@ -424,10 +505,10 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf,
/* When it's the entry of the whole tailcall context,
* zeroing rax means initialising tail_call_cnt.
*/
- EMIT2(0x31, 0xC0); /* xor eax, eax */
+ EMIT3(0x48, 0x31, 0xC0); /* xor rax, rax */
else
/* Keep the same instruction layout. */
- EMIT2(0x66, 0x90); /* nop2 */
+ emit_nops(&prog, 3); /* nop3 */
}
/* Exception callback receives FP as third parameter */
if (is_exception_cb) {
@@ -453,7 +534,7 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf,
if (stack_depth)
EMIT3_off32(0x48, 0x81, 0xEC, round_up(stack_depth, 8));
if (tail_call_reachable)
- EMIT1(0x50); /* push rax */
+ emit_prologue_tail_call(&prog, is_subprog);
*pprog = prog;
}
@@ -589,13 +670,15 @@ static void emit_return(u8 **pprog, u8 *ip)
*pprog = prog;
}
+#define BPF_TAIL_CALL_CNT_PTR_STACK_OFF(stack) (-16 - round_up(stack, 8))
+
/*
* Generate the following code:
*
* ... bpf_tail_call(void *ctx, struct bpf_array *array, u64 index) ...
* if (index >= array->map.max_entries)
* goto out;
- * if (tail_call_cnt++ >= MAX_TAIL_CALL_CNT)
+ * if ((*tcc_ptr)++ >= MAX_TAIL_CALL_CNT)
* goto out;
* prog = array->ptrs[index];
* if (prog == NULL)
@@ -608,7 +691,7 @@ static void emit_bpf_tail_call_indirect(struct bpf_prog *bpf_prog,
u32 stack_depth, u8 *ip,
struct jit_context *ctx)
{
- int tcc_off = -4 - round_up(stack_depth, 8);
+ int tcc_ptr_off = BPF_TAIL_CALL_CNT_PTR_STACK_OFF(stack_depth);
u8 *prog = *pprog, *start = *pprog;
int offset;
@@ -630,16 +713,14 @@ static void emit_bpf_tail_call_indirect(struct bpf_prog *bpf_prog,
EMIT2(X86_JBE, offset); /* jbe out */
/*
- * if (tail_call_cnt++ >= MAX_TAIL_CALL_CNT)
+ * if ((*tcc_ptr)++ >= MAX_TAIL_CALL_CNT)
* goto out;
*/
- EMIT2_off32(0x8B, 0x85, tcc_off); /* mov eax, dword ptr [rbp - tcc_off] */
- EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
+ EMIT3_off32(0x48, 0x8B, 0x85, tcc_ptr_off); /* mov rax, qword ptr [rbp - tcc_ptr_off] */
+ EMIT4(0x48, 0x83, 0x38, MAX_TAIL_CALL_CNT); /* cmp qword ptr [rax], MAX_TAIL_CALL_CNT */
offset = ctx->tail_call_indirect_label - (prog + 2 - start);
EMIT2(X86_JAE, offset); /* jae out */
- EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
- EMIT2_off32(0x89, 0x85, tcc_off); /* mov dword ptr [rbp - tcc_off], eax */
/* prog = array->ptrs[index]; */
EMIT4_off32(0x48, 0x8B, 0x8C, 0xD6, /* mov rcx, [rsi + rdx * 8 + offsetof(...)] */
@@ -654,6 +735,9 @@ static void emit_bpf_tail_call_indirect(struct bpf_prog *bpf_prog,
offset = ctx->tail_call_indirect_label - (prog + 2 - start);
EMIT2(X86_JE, offset); /* je out */
+ /* Inc tail_call_cnt if the slot is populated. */
+ EMIT4(0x48, 0x83, 0x00, 0x01); /* add qword ptr [rax], 1 */
+
if (bpf_prog->aux->exception_boundary) {
pop_callee_regs(&prog, all_callee_regs_used);
pop_r12(&prog);
@@ -663,6 +747,11 @@ static void emit_bpf_tail_call_indirect(struct bpf_prog *bpf_prog,
pop_r12(&prog);
}
+ /* Pop tail_call_cnt_ptr. */
+ EMIT1(0x58); /* pop rax */
+ /* Pop tail_call_cnt, if it's main prog.
+ * Pop tail_call_cnt_ptr, if it's subprog.
+ */
EMIT1(0x58); /* pop rax */
if (stack_depth)
EMIT3_off32(0x48, 0x81, 0xC4, /* add rsp, sd */
@@ -691,21 +780,19 @@ static void emit_bpf_tail_call_direct(struct bpf_prog *bpf_prog,
bool *callee_regs_used, u32 stack_depth,
struct jit_context *ctx)
{
- int tcc_off = -4 - round_up(stack_depth, 8);
+ int tcc_ptr_off = BPF_TAIL_CALL_CNT_PTR_STACK_OFF(stack_depth);
u8 *prog = *pprog, *start = *pprog;
int offset;
/*
- * if (tail_call_cnt++ >= MAX_TAIL_CALL_CNT)
+ * if ((*tcc_ptr)++ >= MAX_TAIL_CALL_CNT)
* goto out;
*/
- EMIT2_off32(0x8B, 0x85, tcc_off); /* mov eax, dword ptr [rbp - tcc_off] */
- EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
+ EMIT3_off32(0x48, 0x8B, 0x85, tcc_ptr_off); /* mov rax, qword ptr [rbp - tcc_ptr_off] */
+ EMIT4(0x48, 0x83, 0x38, MAX_TAIL_CALL_CNT); /* cmp qword ptr [rax], MAX_TAIL_CALL_CNT */
offset = ctx->tail_call_direct_label - (prog + 2 - start);
EMIT2(X86_JAE, offset); /* jae out */
- EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
- EMIT2_off32(0x89, 0x85, tcc_off); /* mov dword ptr [rbp - tcc_off], eax */
poke->tailcall_bypass = ip + (prog - start);
poke->adj_off = X86_TAIL_CALL_OFFSET;
@@ -715,6 +802,9 @@ static void emit_bpf_tail_call_direct(struct bpf_prog *bpf_prog,
emit_jump(&prog, (u8 *)poke->tailcall_target + X86_PATCH_SIZE,
poke->tailcall_bypass);
+ /* Inc tail_call_cnt if the slot is populated. */
+ EMIT4(0x48, 0x83, 0x00, 0x01); /* add qword ptr [rax], 1 */
+
if (bpf_prog->aux->exception_boundary) {
pop_callee_regs(&prog, all_callee_regs_used);
pop_r12(&prog);
@@ -724,6 +814,11 @@ static void emit_bpf_tail_call_direct(struct bpf_prog *bpf_prog,
pop_r12(&prog);
}
+ /* Pop tail_call_cnt_ptr. */
+ EMIT1(0x58); /* pop rax */
+ /* Pop tail_call_cnt, if it's main prog.
+ * Pop tail_call_cnt_ptr, if it's subprog.
+ */
EMIT1(0x58); /* pop rax */
if (stack_depth)
EMIT3_off32(0x48, 0x81, 0xC4, round_up(stack_depth, 8));
@@ -1311,9 +1406,11 @@ static void emit_shiftx(u8 **pprog, u32 dst_reg, u8 src_reg, bool is64, u8 op)
#define INSN_SZ_DIFF (((addrs[i] - addrs[i - 1]) - (prog - temp)))
-/* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */
-#define RESTORE_TAIL_CALL_CNT(stack) \
- EMIT3_off32(0x48, 0x8B, 0x85, -round_up(stack, 8) - 8)
+#define __LOAD_TCC_PTR(off) \
+ EMIT3_off32(0x48, 0x8B, 0x85, off)
+/* mov rax, qword ptr [rbp - rounded_stack_depth - 16] */
+#define LOAD_TAIL_CALL_CNT_PTR(stack) \
+ __LOAD_TCC_PTR(BPF_TAIL_CALL_CNT_PTR_STACK_OFF(stack))
static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image,
int oldproglen, struct jit_context *ctx, bool jmp_padding)
@@ -2031,7 +2128,7 @@ populate_extable:
func = (u8 *) __bpf_call_base + imm32;
if (tail_call_reachable) {
- RESTORE_TAIL_CALL_CNT(bpf_prog->aux->stack_depth);
+ LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
ip += 7;
}
if (!imm32)
@@ -2184,7 +2281,7 @@ emit_cond_jmp: /* Convert BPF opcode to x86 */
return -EFAULT;
}
jmp_offset = addrs[i + insn->off] - addrs[i];
- if (is_imm8(jmp_offset)) {
+ if (is_imm8_jmp_offset(jmp_offset)) {
if (jmp_padding) {
/* To keep the jmp_offset valid, the extra bytes are
* padded before the jump insn, so we subtract the
@@ -2266,7 +2363,7 @@ emit_cond_jmp: /* Convert BPF opcode to x86 */
break;
}
emit_jmp:
- if (is_imm8(jmp_offset)) {
+ if (is_imm8_jmp_offset(jmp_offset)) {
if (jmp_padding) {
/* To avoid breaking jmp_offset, the extra bytes
* are padded before the actual jmp insn, so
@@ -2706,6 +2803,10 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
return 0;
}
+/* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */
+#define LOAD_TRAMP_TAIL_CALL_CNT_PTR(stack) \
+ __LOAD_TCC_PTR(-round_up(stack, 8) - 8)
+
/* Example:
* __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
* its 'struct btf_func_model' will be nr_args=2
@@ -2826,7 +2927,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
* [ ... ]
* [ stack_arg2 ]
* RBP - arg_stack_off [ stack_arg1 ]
- * RSP [ tail_call_cnt ] BPF_TRAMP_F_TAIL_CALL_CTX
+ * RSP [ tail_call_cnt_ptr ] BPF_TRAMP_F_TAIL_CALL_CTX
*/
/* room for return value of orig_call or fentry prog */
@@ -2955,10 +3056,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
save_args(m, &prog, arg_stack_off, true);
if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) {
- /* Before calling the original function, restore the
- * tail_call_cnt from stack to rax.
+ /* Before calling the original function, load the
+ * tail_call_cnt_ptr from stack to rax.
*/
- RESTORE_TAIL_CALL_CNT(stack_size);
+ LOAD_TRAMP_TAIL_CALL_CNT_PTR(stack_size);
}
if (flags & BPF_TRAMP_F_ORIG_STACK) {
@@ -3017,10 +3118,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
goto cleanup;
}
} else if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) {
- /* Before running the original function, restore the
- * tail_call_cnt from stack to rax.
+ /* Before running the original function, load the
+ * tail_call_cnt_ptr from stack to rax.
*/
- RESTORE_TAIL_CALL_CNT(stack_size);
+ LOAD_TRAMP_TAIL_CALL_CNT_PTR(stack_size);
}
/* restore return value of orig_call or fentry prog back into RAX */
generated by cgit v1.2.3-58-ga151 (git 2.39.0) at 2024-11-22 00:20:57 +0000