bpf jit: Let the powerpc jit handle negative offsets

Now the helper function from filter.c for negative offsets is exported,
it can be used it in the jit to handle negative offsets.

First modify the asm load helper functions to handle:
- know positive offsets
- know negative offsets
- any offset

then the compiler can be modified to explicitly use these helper
when appropriate.

This fixes the case of a negative X register and allows to lift
the restriction that bpf programs with negative offsets can't
be jited.

Tested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Jan Seiffert <kaffeemonster@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 17 deletions

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 73619d3aeb6c..2dc8b1484845 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -127,6 +127,9 @@ static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
         PPC_BLR();
 }
 
+#define CHOOSE_LOAD_FUNC(K, func) \
+        ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
+
 /* Assemble the body code between the prologue & epilogue. */
 static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
                               struct codegen_context *ctx,
@@ -391,21 +394,16 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
 
                         /*** Absolute loads from packet header/data ***/
                 case BPF_S_LD_W_ABS:
-                        func = sk_load_word;
+                        func = CHOOSE_LOAD_FUNC(K, sk_load_word);
                         goto common_load;
                 case BPF_S_LD_H_ABS:
-                        func = sk_load_half;
+                        func = CHOOSE_LOAD_FUNC(K, sk_load_half);
                         goto common_load;
                 case BPF_S_LD_B_ABS:
-                        func = sk_load_byte;
+                        func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
                 common_load:
-                        /*
-                         * Load from [K].  Reference with the (negative)
-                         * SKF_NET_OFF/SKF_LL_OFF offsets is unsupported.
-                         */
+                        /* Load from [K]. */
                         ctx->seen |= SEEN_DATAREF;
-                        if ((int)K < 0)
-                                return -ENOTSUPP;
                         PPC_LI64(r_scratch1, func);
                         PPC_MTLR(r_scratch1);
                         PPC_LI32(r_addr, K);
@@ -429,7 +427,7 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
                 common_load_ind:
                         /*
                          * Load from [X + K].  Negative offsets are tested for
-                         * in the helper functions, and result in a 'ret 0'.
+                         * in the helper functions.
                          */
                         ctx->seen |= SEEN_DATAREF | SEEN_XREG;
                         PPC_LI64(r_scratch1, func);
@@ -443,13 +441,7 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
                         break;
 
                 case BPF_S_LDX_B_MSH:
-                        /*
-                         * x86 version drops packet (RET 0) when K<0, whereas
-                         * interpreter does allow K<0 (__load_pointer, special
-                         * ancillary data).  common_load returns ENOTSUPP if K<0,
-                         * so we fall back to interpreter & filter works.
-                         */
-                        func = sk_load_byte_msh;
+                        func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
                         goto common_load;
                         break;