bpf ppc64: Add BPF_PROBE_MEM support for JIT

BPF load instruction with BPF_PROBE_MEM mode can cause a fault
inside kernel. Append exception table for such instructions
within BPF program.

Unlike other archs which uses extable 'fixup' field to pass dest_reg
and nip, BPF exception table on PowerPC follows the generic PowerPC
exception table design, where it populates both fixup and extable
sections within BPF program. fixup section contains two instructions,
first instruction clears dest_reg and 2nd jumps to next instruction
in the BPF code. extable 'insn' field contains relative offset of
the instruction and 'fixup' field contains relative offset of the
fixup entry. Example layout of BPF program with extable present:

             +------------------+
             |                  |
             |                  |
   0x4020 -->| ld   r27,4(r3)   |
             |                  |
             |                  |
   0x40ac -->| lwz  r3,0(r4)    |
             |                  |
             |                  |
             |------------------|
   0x4280 -->| li  r27,0        |  \ fixup entry
             | b   0x4024       |  /
   0x4288 -->| li  r3,0         |
             | b   0x40b0       |
             |------------------|
   0x4290 -->| insn=0xfffffd90  |  \ extable entry
             | fixup=0xffffffec |  /
   0x4298 -->| insn=0xfffffe14  |
             | fixup=0xffffffec |
             +------------------+

   (Addresses shown here are chosen random, not real)

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211012123056.485795-6-hbathini@linux.ibm.com

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index 8b2ac1c27f1f..54e7cef3e1f2 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -268,7 +268,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 
 /* Assemble the body code between the prologue & epilogue */
 int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx,
-		       u32 *addrs)
+		       u32 *addrs, int pass)
 {
 	const struct bpf_insn *insn = fp->insnsi;
 	int flen = fp->len;