diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index b162ad70effcf..7658612d915ca 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -152,8 +152,6 @@ static void build_prologue(struct jit_ctx *ctx)
const u8 r8 = bpf2a64[BPF_REG_8];
const u8 r9 = bpf2a64[BPF_REG_9];
const u8 fp = bpf2a64[BPF_REG_FP];
- const u8 ra = bpf2a64[BPF_REG_A];
- const u8 rx = bpf2a64[BPF_REG_X];
const u8 tmp1 = bpf2a64[TMP_REG_1];
const u8 tmp2 = bpf2a64[TMP_REG_2];
@@ -200,10 +198,6 @@ static void build_prologue(struct jit_ctx *ctx)
/* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, STACK_SIZE), ctx);
-
- /* Clear registers A and X */
- emit_a64_mov_i64(ra, 0, ctx);
- emit_a64_mov_i64(rx, 0, ctx);
}
static void build_epilogue(struct jit_ctx *ctx)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 9a0c4c22e5367..3c0bfc1f26941 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -408,7 +408,7 @@ static void emit_load_skb_data_hlen(struct bpf_jit *jit)
* Save registers and create stack frame if necessary.
* See stack frame layout desription in "bpf_jit.h"!
*/
-static void bpf_jit_prologue(struct bpf_jit *jit, bool is_classic)
+static void bpf_jit_prologue(struct bpf_jit *jit)
{
if (jit->seen & SEEN_TAIL_CALL) {
/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */
@@ -448,15 +448,6 @@ static void bpf_jit_prologue(struct bpf_jit *jit, bool is_classic)
/* stg %b1,ST_OFF_SKBP(%r0,%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0, REG_15,
STK_OFF_SKBP);
- /* Clear A (%b0) and X (%b7) registers for converted BPF programs */
- if (is_classic) {
- if (REG_SEEN(BPF_REG_A))
- /* lghi %ba,0 */
- EMIT4_IMM(0xa7090000, BPF_REG_A, 0);
- if (REG_SEEN(BPF_REG_X))
- /* lghi %bx,0 */
- EMIT4_IMM(0xa7090000, BPF_REG_X, 0);
- }
}
/*
@@ -1245,7 +1236,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp)
jit->lit = jit->lit_start;
jit->prg = 0;
- bpf_jit_prologue(jit, bpf_prog_was_classic(fp));
+ bpf_jit_prologue(jit);
for (i = 0; i < fp->len; i += insn_count) {
insn_count = bpf_jit_insn(jit, fp, i);
if (insn_count < 0)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 75991979f667f..c080e812ce85a 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -193,7 +193,7 @@ struct jit_context {
32 /* space for rbx, r13, r14, r15 */ + \
8 /* space for skb_copy_bits() buffer */)
-#define PROLOGUE_SIZE 51
+#define PROLOGUE_SIZE 48
/* emit x64 prologue code for BPF program and check it's size.
* bpf_tail_call helper will skip it while jumping into another program
@@ -229,11 +229,15 @@ static void emit_prologue(u8 **pprog)
/* mov qword ptr [rbp-X],r15 */
EMIT3_off32(0x4C, 0x89, 0xBD, -STACKSIZE + 24);
- /* clear A and X registers */
- EMIT2(0x31, 0xc0); /* xor eax, eax */
- EMIT3(0x4D, 0x31, 0xED); /* xor r13, r13 */
+ /* Clear the tail call counter (tail_call_cnt): for eBPF tail calls
+ * we need to reset the counter to 0. It's done in two instructions,
+ * resetting rax register to 0 (xor on eax gets 0 extended), and
+ * moving it to the counter location.
+ */
- /* clear tail_cnt: mov qword ptr [rbp-X], rax */
+ /* xor eax, eax */
+ EMIT2(0x31, 0xc0);
+ /* mov qword ptr [rbp-X], rax */
EMIT3_off32(0x48, 0x89, 0x85, -STACKSIZE + 32);
BUILD_BUG_ON(cnt != PROLOGUE_SIZE);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 334b1bdd572c1..972d9a8e4ac4d 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -306,10 +306,6 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
FP = (u64) (unsigned long) &stack[ARRAY_SIZE(stack)];
ARG1 = (u64) (unsigned long) ctx;
- /* Registers used in classic BPF programs need to be reset first. */
- regs[BPF_REG_A] = 0;
- regs[BPF_REG_X] = 0;
-
select_insn:
goto *jumptable[insn->code];
diff --git a/net/core/filter.c b/net/core/filter.c
index 34bf6fc77c1de..b513eb8718398 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -381,9 +381,22 @@ static int bpf_convert_filter(struct sock_filter *prog, int len,
new_insn = new_prog;
fp = prog;
- if (new_insn)
- *new_insn = BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1);
- new_insn++;
+ /* Classic BPF related prologue emission. */
+ if (new_insn) {
+ /* Classic BPF expects A and X to be reset first. These need
+ * to be guaranteed to be the first two instructions.
+ */
+ *new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_A, BPF_REG_A);
+ *new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_X, BPF_REG_X);
+
+ /* All programs must keep CTX in callee saved BPF_REG_CTX.
+ * In eBPF case it's done by the compiler, here we need to
+ * do this ourself. Initial CTX is present in BPF_REG_ARG1.
+ */
+ *new_insn++ = BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1);
+ } else {
+ new_insn += 3;
+ }
for (i = 0; i < len; fp++, i++) {
struct bpf_insn tmp_insns[6] = { };