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, 60 insertions, 6 deletions

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index f39ad8d123dd..a936dca7331e 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -101,6 +101,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	struct bpf_prog *tmp_fp;
 	bool bpf_blinded = false;
 	bool extra_pass = false;
+	u32 extable_len;
+	u32 fixup_len;
 
 	if (!fp->jit_requested)
 		return org_fp;
@@ -131,7 +133,6 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 		image = jit_data->image;
 		bpf_hdr = jit_data->header;
 		proglen = jit_data->proglen;
-		alloclen = proglen + FUNCTION_DESCR_SIZE;
 		extra_pass = true;
 		goto skip_init_ctx;
 	}
@@ -149,7 +150,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
 
 	/* Scouting faux-generate pass 0 */
-	if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
+	if (bpf_jit_build_body(fp, 0, &cgctx, addrs, 0)) {
 		/* We hit something illegal or unsupported. */
 		fp = org_fp;
 		goto out_addrs;
@@ -162,7 +163,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	 */
 	if (cgctx.seen & SEEN_TAILCALL) {
 		cgctx.idx = 0;
-		if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
+		if (bpf_jit_build_body(fp, 0, &cgctx, addrs, 0)) {
 			fp = org_fp;
 			goto out_addrs;
 		}
@@ -177,8 +178,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	bpf_jit_build_prologue(0, &cgctx);
 	bpf_jit_build_epilogue(0, &cgctx);
 
+	fixup_len = fp->aux->num_exentries * BPF_FIXUP_LEN * 4;
+	extable_len = fp->aux->num_exentries * sizeof(struct exception_table_entry);
+
 	proglen = cgctx.idx * 4;
-	alloclen = proglen + FUNCTION_DESCR_SIZE;
+	alloclen = proglen + FUNCTION_DESCR_SIZE + fixup_len + extable_len;
 
 	bpf_hdr = bpf_jit_binary_alloc(alloclen, &image, 4, bpf_jit_fill_ill_insns);
 	if (!bpf_hdr) {
@@ -186,6 +190,9 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 		goto out_addrs;
 	}
 
+	if (extable_len)
+		fp->aux->extable = (void *)image + FUNCTION_DESCR_SIZE + proglen + fixup_len;
+
 skip_init_ctx:
 	code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
 
@@ -210,7 +217,7 @@ skip_init_ctx:
 		/* Now build the prologue, body code & epilogue for real. */
 		cgctx.idx = 0;
 		bpf_jit_build_prologue(code_base, &cgctx);
-		if (bpf_jit_build_body(fp, code_base, &cgctx, addrs)) {
+		if (bpf_jit_build_body(fp, code_base, &cgctx, addrs, pass)) {
 			bpf_jit_binary_free(bpf_hdr);
 			fp = org_fp;
 			goto out_addrs;
@@ -238,7 +245,7 @@ skip_codegen_passes:
 
 	fp->bpf_func = (void *)image;
 	fp->jited = 1;
-	fp->jited_len = alloclen;
+	fp->jited_len = proglen + FUNCTION_DESCR_SIZE;
 
 	bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
 	if (!fp->is_func || extra_pass) {
@@ -262,3 +269,50 @@ out:
 
 	return fp;
 }
+
+/*
+ * The caller should check for (BPF_MODE(code) == BPF_PROBE_MEM) before calling
+ * this function, as this only applies to BPF_PROBE_MEM, for now.
+ */
+int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct codegen_context *ctx,
+			  int insn_idx, int jmp_off, int dst_reg)
+{
+	off_t offset;
+	unsigned long pc;
+	struct exception_table_entry *ex;
+	u32 *fixup;
+
+	/* Populate extable entries only in the last pass */
+	if (pass != 2)
+		return 0;
+
+	if (!fp->aux->extable ||
+	    WARN_ON_ONCE(ctx->exentry_idx >= fp->aux->num_exentries))
+		return -EINVAL;
+
+	pc = (unsigned long)&image[insn_idx];
+
+	fixup = (void *)fp->aux->extable -
+		(fp->aux->num_exentries * BPF_FIXUP_LEN * 4) +
+		(ctx->exentry_idx * BPF_FIXUP_LEN * 4);
+
+	fixup[0] = PPC_RAW_LI(dst_reg, 0);
+
+	fixup[BPF_FIXUP_LEN - 1] =
+		PPC_RAW_BRANCH((long)(pc + jmp_off) - (long)&fixup[BPF_FIXUP_LEN - 1]);
+
+	ex = &fp->aux->extable[ctx->exentry_idx];
+
+	offset = pc - (long)&ex->insn;
+	if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN))
+		return -ERANGE;
+	ex->insn = offset;
+
+	offset = (long)fixup - (long)&ex->fixup;
+	if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN))
+		return -ERANGE;
+	ex->fixup = offset;
+
+	ctx->exentry_idx++;
+	return 0;
+}