bpf: move tmp variable into ax register in interpreter

This change moves the on-stack 64 bit tmp variable in ___bpf_prog_run()
into the hidden ax register. The latter is currently only used in JITs
for constant blinding as a temporary scratch register, meaning the BPF
interpreter will never see the use of ax. Therefore it is safe to use
it for the cases where tmp has been used earlier. This is needed to later
on allow restricted hidden use of ax in both interpreter and JITs.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 8c8544b375ebd93cea7d2b66e1384db2041232cd..84a6a98f8328688eab4fe046f6b169a7a062472f 100644 (file)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -60,7 +60,8 @@ struct sock_reuseport;
  * constants. See JIT pre-step in bpf_jit_blind_constants().
  */
 #define BPF_REG_AX             MAX_BPF_REG
-#define MAX_BPF_JIT_REG                (MAX_BPF_REG + 1)
+#define MAX_BPF_EXT_REG                (MAX_BPF_REG + 1)
+#define MAX_BPF_JIT_REG                MAX_BPF_EXT_REG
 
 /* unused opcode to mark special call to bpf_tail_call() helper */
 #define BPF_TAIL_CALL  0xf0

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 38de580abcc25bd5dbf44fb9fcfbf8fb19692434..a34312a5eea23ba9cbd8f9d2e391016f95c009a9 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -54,6 +54,7 @@
 #define DST    regs[insn->dst_reg]
 #define SRC    regs[insn->src_reg]
 #define FP     regs[BPF_REG_FP]
+#define AX     regs[BPF_REG_AX]
 #define ARG1   regs[BPF_REG_ARG1]
 #define CTX    regs[BPF_REG_CTX]
 #define IMM    insn->imm
@@ -1188,7 +1189,6 @@ bool bpf_opcode_in_insntable(u8 code)
  */
 static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
 {
-       u64 tmp;
 #define BPF_INSN_2_LBL(x, y)    [BPF_##x | BPF_##y] = &&x##_##y
 #define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z
        static const void *jumptable[256] = {
@@ -1268,36 +1268,36 @@ select_insn:
                (*(s64 *) &DST) >>= IMM;
                CONT;
        ALU64_MOD_X:
-               div64_u64_rem(DST, SRC, &tmp);
-               DST = tmp;
+               div64_u64_rem(DST, SRC, &AX);
+               DST = AX;
                CONT;
        ALU_MOD_X:
-               tmp = (u32) DST;
-               DST = do_div(tmp, (u32) SRC);
+               AX = (u32) DST;
+               DST = do_div(AX, (u32) SRC);
                CONT;
        ALU64_MOD_K:
-               div64_u64_rem(DST, IMM, &tmp);
-               DST = tmp;
+               div64_u64_rem(DST, IMM, &AX);
+               DST = AX;
                CONT;
        ALU_MOD_K:
-               tmp = (u32) DST;
-               DST = do_div(tmp, (u32) IMM);
+               AX = (u32) DST;
+               DST = do_div(AX, (u32) IMM);
                CONT;
        ALU64_DIV_X:
                DST = div64_u64(DST, SRC);
                CONT;
        ALU_DIV_X:
-               tmp = (u32) DST;
-               do_div(tmp, (u32) SRC);
-               DST = (u32) tmp;
+               AX = (u32) DST;
+               do_div(AX, (u32) SRC);
+               DST = (u32) AX;
                CONT;
        ALU64_DIV_K:
                DST = div64_u64(DST, IMM);
                CONT;
        ALU_DIV_K:
-               tmp = (u32) DST;
-               do_div(tmp, (u32) IMM);
-               DST = (u32) tmp;
+               AX = (u32) DST;
+               do_div(AX, (u32) IMM);
+               DST = (u32) AX;
                CONT;
        ALU_END_TO_BE:
                switch (IMM) {
@@ -1553,7 +1553,7 @@ STACK_FRAME_NON_STANDARD(___bpf_prog_run); /* jump table */
 static unsigned int PROG_NAME(stack_size)(const void *ctx, const struct bpf_insn *insn) \
 { \
        u64 stack[stack_size / sizeof(u64)]; \
-       u64 regs[MAX_BPF_REG]; \
+       u64 regs[MAX_BPF_EXT_REG]; \
 \
        FP = (u64) (unsigned long) &stack[ARRAY_SIZE(stack)]; \
        ARG1 = (u64) (unsigned long) ctx; \
@@ -1566,7 +1566,7 @@ static u64 PROG_NAME_ARGS(stack_size)(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5, \
                                      const struct bpf_insn *insn) \
 { \
        u64 stack[stack_size / sizeof(u64)]; \
-       u64 regs[MAX_BPF_REG]; \
+       u64 regs[MAX_BPF_EXT_REG]; \
 \
        FP = (u64) (unsigned long) &stack[ARRAY_SIZE(stack)]; \
        BPF_R1 = r1; \