MIPS: bpf: Drop update_on_xread and always initialize the X register

Previously, update_on_xread() only set the reset flag if SEEN_X hasn't
been set already. However, SEEN_X is used to indicate that X is used
as destination or source register so there are some cases where X
is only used as source register and we really need to make sure that it
has been initialized in time. As a result of which, drop this function and
always set X to zero if it's used in any of the opcodes.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: netdev@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7133/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 1 insertions, 21 deletions

diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 00c4c83972bb..1bcd599d9971 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -119,8 +119,6 @@
 /* Arguments used by JIT */
 #define ARGS_USED_BY_JIT        2 /* only applicable to 64-bit */
 
-#define FLAG_NEED_X_RESET       (1 << 0)
-
 #define SBIT(x)                 (1 << (x)) /* Signed version of BIT() */
 
 /**
@@ -549,14 +547,6 @@ static inline u16 align_sp(unsigned int num)
         return num;
 }
 
-static inline void update_on_xread(struct jit_ctx *ctx)
-{
-        if (!(ctx->flags & SEEN_X))
-                ctx->flags |= FLAG_NEED_X_RESET;
-
-        ctx->flags |= SEEN_X;
-}
-
 static bool is_load_to_a(u16 inst)
 {
         switch (inst) {
@@ -701,7 +691,7 @@ static void build_prologue(struct jit_ctx *ctx)
         if (ctx->flags & SEEN_SKB)
                 emit_reg_move(r_skb, MIPS_R_A0, ctx);
 
-        if (ctx->flags & FLAG_NEED_X_RESET)
+        if (ctx->flags & SEEN_X)
                 emit_jit_reg_move(r_X, r_zero, ctx);
 
         /* Do not leak kernel data to userspace */
@@ -876,7 +866,6 @@ load_common:
                         /* A <- P[X + k:1] */
                         load_order = 0;
 load_ind:
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_OFF | SEEN_X;
                         emit_addiu(r_off, r_X, k, ctx);
                         goto load_common;
@@ -972,7 +961,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_MUL | BPF_X:
                         /* A *= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_A | SEEN_X;
                         emit_mul(r_A, r_A, r_X, ctx);
                         break;
@@ -1002,7 +990,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_DIV | BPF_X:
                         /* A /= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_X | SEEN_A;
                         /* Check if r_X is zero */
                         emit_bcond(MIPS_COND_EQ, r_X, r_zero,
@@ -1012,7 +999,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_MOD | BPF_X:
                         /* A %= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_X | SEEN_A;
                         /* Check if r_X is zero */
                         emit_bcond(MIPS_COND_EQ, r_X, r_zero,
@@ -1027,7 +1013,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_OR | BPF_X:
                         /* A |= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_A;
                         emit_ori(r_A, r_A, r_X, ctx);
                         break;
@@ -1039,7 +1024,6 @@ load_ind:
                 case BPF_ANC | SKF_AD_ALU_XOR_X:
                 case BPF_ALU | BPF_XOR | BPF_X:
                         /* A ^= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_A;
                         emit_xor(r_A, r_A, r_X, ctx);
                         break;
@@ -1050,7 +1034,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_AND | BPF_X:
                         /* A &= X */
-                        update_on_xread(ctx);
                         ctx->flags |= SEEN_A | SEEN_X;
                         emit_and(r_A, r_A, r_X, ctx);
                         break;
@@ -1062,7 +1045,6 @@ load_ind:
                 case BPF_ALU | BPF_LSH | BPF_X:
                         /* A <<= X */
                         ctx->flags |= SEEN_A | SEEN_X;
-                        update_on_xread(ctx);
                         emit_sllv(r_A, r_A, r_X, ctx);
                         break;
                 case BPF_ALU | BPF_RSH | BPF_K:
@@ -1072,7 +1054,6 @@ load_ind:
                         break;
                 case BPF_ALU | BPF_RSH | BPF_X:
                         ctx->flags |= SEEN_A | SEEN_X;
-                        update_on_xread(ctx);
                         emit_srlv(r_A, r_A, r_X, ctx);
                         break;
                 case BPF_ALU | BPF_NEG:
@@ -1243,7 +1224,6 @@ jmp_cmp:
                 case BPF_MISC | BPF_TXA:
                         /* A = X */
                         ctx->flags |= SEEN_A | SEEN_X;
-                        update_on_xread(ctx);
                         emit_jit_reg_move(r_A, r_X, ctx);
                         break;
                 /* AUX */