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bpf ppc64: Add BPF_PROBE_MEM support for JIT

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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
This commit is contained in:
Ravi Bangoria 2021-10-12 18:00:53 +05:30 committed by Michael Ellerman
parent f15a71b388
commit 983bdc0245
4 changed files with 80 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/powerpc/net/bpf_jit.h
View File

@ -150,8 +150,11 @@ struct codegen_context {
unsigned int idx;
unsigned int stack_size;
int b2p[ARRAY_SIZE(b2p)];
unsigned int exentry_idx;
};
#define BPF_FIXUP_LEN 2 /* Two instructions => 8 bytes */
static inline void bpf_flush_icache(void *start, void *end)
{
smp_wmb(); /* smp write barrier */
@ -175,11 +178,14 @@ static inline void bpf_clear_seen_register(struct codegen_context *ctx, int i)
void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func);
int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx,
u32 *addrs);
u32 *addrs, int pass);
void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx);
void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx);
void bpf_jit_realloc_regs(struct codegen_context *ctx);
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);
#endif
#endif

66
arch/powerpc/net/bpf_jit_comp.c
View File

@ -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;
}

2
arch/powerpc/net/bpf_jit_comp32.c
View File

@ -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;

13
arch/powerpc/net/bpf_jit_comp64.c
View File

@ -297,7 +297,7 @@ asm (
/* 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)
{
enum stf_barrier_type stf_barrier = stf_barrier_type_get();
const struct bpf_insn *insn = fp->insnsi;
@ -779,12 +779,16 @@ emit_clear:
*/
/* dst = *(u8 *)(ul) (src + off) */
case BPF_LDX | BPF_MEM | BPF_B:
case BPF_LDX | BPF_PROBE_MEM | BPF_B:
/* dst = *(u16 *)(ul) (src + off) */
case BPF_LDX | BPF_MEM | BPF_H:
case BPF_LDX | BPF_PROBE_MEM | BPF_H:
/* dst = *(u32 *)(ul) (src + off) */
case BPF_LDX | BPF_MEM | BPF_W:
case BPF_LDX | BPF_PROBE_MEM | BPF_W:
/* dst = *(u64 *)(ul) (src + off) */
case BPF_LDX | BPF_MEM | BPF_DW:
case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
switch (size) {
case BPF_B:
EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off));
@ -802,6 +806,13 @@ emit_clear:
if (size != BPF_DW && insn_is_zext(&insn[i + 1]))
addrs[++i] = ctx->idx * 4;
if (BPF_MODE(code) == BPF_PROBE_MEM) {
ret = bpf_add_extable_entry(fp, image, pass, ctx, ctx->idx - 1,
4, dst_reg);
if (ret)
return ret;
}
break;
/*