sparc: bpf_jit: fix loads from negative offsets

- fix BPF_LD|ABS|IND from negative offsets:
  make sure to sign extend lower 32 bits in 64-bit register
  before calling C helpers from JITed code, otherwise 'int k'
  argument of bpf_internal_load_pointer_neg_helper() function
  will be added as large unsigned integer, causing packet size
  check to trigger and abort the program.

  It's worth noting that JITed code for 'A = A op K' will affect
  upper 32 bits differently depending whether K is simm13 or not.
  Since small constants are sign extended, whereas large constants
  are stored in temp register and zero extended.
  That is ok and we don't have to pay a penalty of sign extension
  for every sethi, since all classic BPF instructions have 32-bit
  semantics and we only need to set correct upper bits when
  transitioning from JITed code into C.

- though instructions 'A &= 0' and 'A *= 0' are odd, JIT compiler
  should not optimize them out

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/sparc/net/bpf_jit_asm.S b/arch/sparc/net/bpf_jit_asm.S
index 9d016c7..8c83f4b 100644
--- a/arch/sparc/net/bpf_jit_asm.S
+++ b/arch/sparc/net/bpf_jit_asm.S
@@ -6,10 +6,12 @@
 #define SAVE_SZ		176
 #define SCRATCH_OFF	STACK_BIAS + 128
 #define BE_PTR(label)	be,pn %xcc, label
+#define SIGN_EXTEND(reg)	sra reg, 0, reg
 #else
 #define SAVE_SZ		96
 #define SCRATCH_OFF	72
 #define BE_PTR(label)	be label
+#define SIGN_EXTEND(reg)
 #endif
 
 #define SKF_MAX_NEG_OFF	(-0x200000) /* SKF_LL_OFF from filter.h */
@@ -135,6 +137,7 @@ bpf_slow_path_byte_msh:
 	save	%sp, -SAVE_SZ, %sp;			\
 	mov	%i0, %o0;				\
 	mov	r_OFF, %o1;				\
+	SIGN_EXTEND(%o1);				\
 	call	bpf_internal_load_pointer_neg_helper;	\
 	 mov	(LEN), %o2;				\
 	mov	%o0, r_TMP;				\