[PATCH v6 bpf-next 7/7] bpf, x86_64: use bpf_prog_pack allocator

From: Song Liu
Date: Fri Jan 21 2022 - 14:50:08 EST

From: Song Liu <songliubraving@xxxxxx>

Use bpf_prog_pack allocator in x86_64 jit.

The program header from bpf_prog_pack is read only during the jit process.
Therefore, the binary is first written to a temporary buffer, and later
copied to final location with text_poke_copy().

Similarly, jit_fill_hole() is updated to fill the hole with 0xcc using
text_poke_copy().

Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 141 ++++++++++++++++++++++++++++--------
1 file changed, 111 insertions(+), 30 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index fe4f08e25a1d..fcdfec992184 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -216,11 +216,32 @@ static u8 simple_alu_opcodes[] = {
[BPF_ARSH] = 0xF8,
};

+#define BPF_X86_JIT_HOLE_BUFFER_SIZE 128
+static char jit_hole_buffer[BPF_X86_JIT_HOLE_BUFFER_SIZE] = {};
+
static void jit_fill_hole(void *area, unsigned int size)
+{
+ struct bpf_binary_header *hdr = area;
+
+ /* fill the first and last 128 bytes of the buffer with INT3 */
+ text_poke_copy(area, jit_hole_buffer, BPF_X86_JIT_HOLE_BUFFER_SIZE);
+ text_poke_copy(area + size - BPF_X86_JIT_HOLE_BUFFER_SIZE,
+ jit_hole_buffer, BPF_X86_JIT_HOLE_BUFFER_SIZE);
+
+ /*
+ * bpf_jit_binary_alloc_pack cannot write size directly to the ro
+ * mapping. Write it here with text_poke_copy().
+ */
+ text_poke_copy(&hdr->size, &size, sizeof(size));
+}
+
+static int __init x86_jit_fill_hole_init(void)
{
/* Fill whole space with INT3 instructions */
- memset(area, 0xcc, size);
+ memset(jit_hole_buffer, 0xcc, BPF_X86_JIT_HOLE_BUFFER_SIZE);
+ return 0;
}
+pure_initcall(x86_jit_fill_hole_init);

struct jit_context {
int cleanup_addr; /* Epilogue code offset */
@@ -361,14 +382,11 @@ static int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,

ret = -EBUSY;
mutex_lock(&text_mutex);
- if (memcmp(ip, old_insn, X86_PATCH_SIZE))
+ if (text_live && memcmp(ip, old_insn, X86_PATCH_SIZE))
goto out;
ret = 1;
if (memcmp(ip, new_insn, X86_PATCH_SIZE)) {
- if (text_live)
- text_poke_bp(ip, new_insn, X86_PATCH_SIZE, NULL);
- else
- memcpy(ip, new_insn, X86_PATCH_SIZE);
+ text_poke_bp(ip, new_insn, X86_PATCH_SIZE, NULL);
ret = 0;
}
out:
@@ -537,7 +555,7 @@ static void emit_bpf_tail_call_direct(struct bpf_jit_poke_descriptor *poke,
*pprog = prog;
}

-static void bpf_tail_call_direct_fixup(struct bpf_prog *prog)
+static void bpf_tail_call_direct_fixup(struct bpf_prog *prog, bool text_live)
{
struct bpf_jit_poke_descriptor *poke;
struct bpf_array *array;
@@ -558,24 +576,15 @@ static void bpf_tail_call_direct_fixup(struct bpf_prog *prog)
mutex_lock(&array->aux->poke_mutex);
target = array->ptrs[poke->tail_call.key];
if (target) {
- /* Plain memcpy is used when image is not live yet
- * and still not locked as read-only. Once poke
- * location is active (poke->tailcall_target_stable),
- * any parallel bpf_arch_text_poke() might occur
- * still on the read-write image until we finally
- * locked it as read-only. Both modifications on
- * the given image are under text_mutex to avoid
- * interference.
- */
ret = __bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP, NULL,
(u8 *)target->bpf_func +
- poke->adj_off, false);
+ poke->adj_off, text_live);
BUG_ON(ret < 0);
ret = __bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
(u8 *)poke->tailcall_target +
- X86_PATCH_SIZE, NULL, false);
+ X86_PATCH_SIZE, NULL, text_live);
BUG_ON(ret < 0);
}
WRITE_ONCE(poke->tailcall_target_stable, true);
@@ -867,7 +876,7 @@ static void emit_nops(u8 **pprog, int len)

#define INSN_SZ_DIFF (((addrs[i] - addrs[i - 1]) - (prog - temp)))

-static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
+static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image,
int oldproglen, struct jit_context *ctx, bool jmp_padding)
{
bool tail_call_reachable = bpf_prog->aux->tail_call_reachable;
@@ -894,8 +903,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
push_callee_regs(&prog, callee_regs_used);

ilen = prog - temp;
- if (image)
- memcpy(image + proglen, temp, ilen);
+ if (rw_image)
+ memcpy(rw_image + proglen, temp, ilen);
proglen += ilen;
addrs[0] = proglen;
prog = temp;
@@ -1324,8 +1333,10 @@ st: if (is_imm8(insn->off))
pr_err("extable->insn doesn't fit into 32-bit\n");
return -EFAULT;
}
- ex->insn = delta;
+ /* switch ex to temporary buffer for writes */
+ ex = (void *)rw_image + ((void *)ex - (void *)image);

+ ex->insn = delta;
ex->type = EX_TYPE_BPF;

if (dst_reg > BPF_REG_9) {
@@ -1706,7 +1717,7 @@ st: if (is_imm8(insn->off))
pr_err("bpf_jit: fatal error\n");
return -EFAULT;
}
- memcpy(image + proglen, temp, ilen);
+ memcpy(rw_image + proglen, temp, ilen);
}
proglen += ilen;
addrs[i] = proglen;
@@ -2248,6 +2259,12 @@ int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs)

struct x64_jit_data {
struct bpf_binary_header *header;
+ /*
+ * With bpf_prog_pack, header points to read-only memory.
+ * rw_header holds a temporary rw buffer for JIT. When JIT is done,
+ * the binary is copied to header with text_poke_copy().
+ */
+ struct bpf_binary_header *rw_header;
int *addrs;
u8 *image;
int proglen;
@@ -2259,6 +2276,7 @@ struct x64_jit_data {

struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
{
+ struct bpf_binary_header *rw_header = NULL;
struct bpf_binary_header *header = NULL;
struct bpf_prog *tmp, *orig_prog = prog;
struct x64_jit_data *jit_data;
@@ -2267,6 +2285,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
bool tmp_blinded = false;
bool extra_pass = false;
bool padding = false;
+ u8 *rw_image = NULL;
u8 *image = NULL;
int *addrs;
int pass;
@@ -2302,6 +2321,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
oldproglen = jit_data->proglen;
image = jit_data->image;
header = jit_data->header;
+ rw_header = jit_data->rw_header;
+ rw_image = (void *)rw_header + ((void *)image - (void *)header);
extra_pass = true;
padding = true;
goto skip_init_addrs;
@@ -2332,14 +2353,18 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
for (pass = 0; pass < MAX_PASSES || image; pass++) {
if (!padding && pass >= PADDING_PASSES)
padding = true;
- proglen = do_jit(prog, addrs, image, oldproglen, &ctx, padding);
+ proglen = do_jit(prog, addrs, image, rw_image, oldproglen, &ctx, padding);
if (proglen <= 0) {
out_image:
image = NULL;
- if (header)
- bpf_jit_binary_free(header);
+ rw_image = NULL;
+ if (header) {
+ bpf_jit_binary_free_pack(header);
+ kfree(rw_header);
+ }
prog = orig_prog;
header = NULL;
+ rw_header = NULL;
goto out_addrs;
}
if (image) {
@@ -2362,12 +2387,34 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
sizeof(struct exception_table_entry);

/* allocate module memory for x86 insns and extable */
- header = bpf_jit_binary_alloc(roundup(proglen, align) + extable_size,
- &image, align, jit_fill_hole);
+ header = bpf_jit_binary_alloc_pack(roundup(proglen, align) + extable_size,
+ &image, align, jit_fill_hole);
if (!header) {
prog = orig_prog;
goto out_addrs;
}
+ if (header->size > bpf_prog_pack_max_size()) {
+ rw_header = header;
+ rw_image = image;
+ } else {
+ /*
+ * With bpf_prog_pack, header and image
+ * points to read-only memory. Allocate a
+ * rw buffer for writes during JIT.
+ *
+ * When the JIT is done, the binary is copied
+ * to header with text_poke_copy().
+ */
+ rw_header = kvmalloc(header->size, GFP_KERNEL | __GFP_ZERO);
+ if (!rw_header) {
+ bpf_jit_binary_free_pack(header);
+ header = NULL;
+ prog = orig_prog;
+ goto out_addrs;
+ }
+ rw_header->size = header->size;
+ rw_image = (void *)rw_header + ((void *)image - (void *)header);
+ }
prog->aux->extable = (void *) image + roundup(proglen, align);
}
oldproglen = proglen;
@@ -2379,14 +2426,23 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)

if (image) {
if (!prog->is_func || extra_pass) {
- bpf_tail_call_direct_fixup(prog);
- bpf_jit_binary_lock_ro(header);
+ if (header->size > bpf_prog_pack_max_size()) {
+ /*
+ * bpf_prog_pack cannot handle too big
+ * program (> ~2MB). Fall back to regular
+ * module_alloc(), and do the fixup and
+ * lock_ro here.
+ */
+ bpf_tail_call_direct_fixup(prog, false);
+ bpf_jit_binary_lock_ro(header);
+ }
} else {
jit_data->addrs = addrs;
jit_data->ctx = ctx;
jit_data->proglen = proglen;
jit_data->image = image;
jit_data->header = header;
+ jit_data->rw_header = rw_header;
}
prog->bpf_func = (void *)image;
prog->jited = 1;
@@ -2402,6 +2458,17 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
kvfree(addrs);
kfree(jit_data);
prog->aux->jit_data = NULL;
+ jit_data = NULL;
+ if (rw_header != header) {
+ text_poke_copy(header, rw_header, header->size);
+ kvfree(rw_header);
+ /*
+ * Do the fixup after final text_poke_copy().
+ * Otherwise, the fix up will be overwritten by
+ * text_poke_copy().
+ */
+ bpf_tail_call_direct_fixup(prog, true);
+ }
}
out:
if (tmp_blinded)
@@ -2415,3 +2482,17 @@ bool bpf_jit_supports_kfunc_call(void)
{
return true;
}
+
+void bpf_jit_free(struct bpf_prog *fp)
+{
+ if (fp->jited) {
+ struct bpf_binary_header *hdr = bpf_jit_binary_hdr(fp);
+
+ if (hdr->size > bpf_prog_pack_max_size())
+ bpf_jit_binary_free(hdr);
+ else
+ bpf_jit_binary_free_pack(hdr);
+ }
+
+ bpf_prog_unlock_free(fp);
+}
--
2.30.2