[PATCH AUTOSEL 6.0 70/77] bpf: use bpf_prog_pack for bpf_dispatcher

Sasha Levin
2022-10-09T22:24:35Z

From: Song Liu <song@kernel.org>

[ Upstream commit 19c02415da2345d0dda2b5c4495bc17cc14b18b5 ]

Allocate bpf_dispatcher with bpf_prog_pack_alloc so that bpf_dispatcher
can share pages with bpf programs.

arch_prepare_bpf_dispatcher() is updated to provide a RW buffer as working
area for arch code to write to.

This also fixes CPA W^X warnning like:

CPA refuse W^X violation: 8000000000000163 -> 0000000000000163 range: ...

Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20220926184739.3512547-2-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/net/bpf_jit_comp.c | 16 ++++++++--------
include/linux/bpf.h | 3 ++-
include/linux/filter.h | 5 +++++
kernel/bpf/core.c | 9 +++++++--
kernel/bpf/dispatcher.c | 27 +++++++++++++++++++++------
5 files changed, 43 insertions(+), 17 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index c1f6c1c51d99..362562c832e6 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2209,7 +2209,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
return ret;
}

-static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs)
+static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs, u8 *image, u8 *buf)
{
u8 *jg_reloc, *prog = *pprog;
int pivot, err, jg_bytes = 1;
@@ -2225,12 +2225,12 @@ static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs)
EMIT2_off32(0x81, add_1reg(0xF8, BPF_REG_3),
progs[a]);
err = emit_cond_near_jump(&prog, /* je func */
- (void *)progs[a], prog,
+ (void *)progs[a], image + (prog - buf),
X86_JE);
if (err)
return err;

- emit_indirect_jump(&prog, 2 /* rdx */, prog);
+ emit_indirect_jump(&prog, 2 /* rdx */, image + (prog - buf));

*pprog = prog;
return 0;
@@ -2255,7 +2255,7 @@ static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs)
jg_reloc = prog;

err = emit_bpf_dispatcher(&prog, a, a + pivot, /* emit lower_part */
- progs);
+ progs, image, buf);
if (err)
return err;

@@ -2269,7 +2269,7 @@ static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs)
emit_code(jg_reloc - jg_bytes, jg_offset, jg_bytes);

err = emit_bpf_dispatcher(&prog, a + pivot + 1, /* emit upper_part */
- b, progs);
+ b, progs, image, buf);
if (err)
return err;

@@ -2289,12 +2289,12 @@ static int cmp_ips(const void *a, const void *b)
return 0;
}

-int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs)
+int arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_funcs)
{
- u8 *prog = image;
+ u8 *prog = buf;

sort(funcs, num_funcs, sizeof(funcs[0]), cmp_ips, NULL);
- return emit_bpf_dispatcher(&prog, 0, num_funcs - 1, funcs);
+ return emit_bpf_dispatcher(&prog, 0, num_funcs - 1, funcs, image, buf);
}

struct x64_jit_data {
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 20c26aed7896..80fc8a88c610 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -891,6 +891,7 @@ struct bpf_dispatcher {
struct bpf_dispatcher_prog progs[BPF_DISPATCHER_MAX];
int num_progs;
void *image;
+ void *rw_image;
u32 image_off;
struct bpf_ksym ksym;
};
@@ -909,7 +910,7 @@ int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampolin
struct bpf_trampoline *bpf_trampoline_get(u64 key,
struct bpf_attach_target_info *tgt_info);
void bpf_trampoline_put(struct bpf_trampoline *tr);
-int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs);
+int arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_funcs);
#define BPF_DISPATCHER_INIT(_name) { \
.mutex = __MUTEX_INITIALIZER(_name.mutex), \
.func = &_name##_func, \
diff --git a/include/linux/filter.h b/include/linux/filter.h
index a5f21dc3c432..f2c47df5ad2a 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1018,6 +1018,8 @@ extern long bpf_jit_limit_max;

typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);

+void bpf_jit_fill_hole_with_zero(void *area, unsigned int size);
+
struct bpf_binary_header *
bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
unsigned int alignment,
@@ -1030,6 +1032,9 @@ void bpf_jit_free(struct bpf_prog *fp);
struct bpf_binary_header *
bpf_jit_binary_pack_hdr(const struct bpf_prog *fp);

+void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns);
+void bpf_prog_pack_free(struct bpf_binary_header *hdr);
+
static inline bool bpf_prog_kallsyms_verify_off(const struct bpf_prog *fp)
{
return list_empty(&fp->aux->ksym.lnode) ||
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 3d9eb3ae334c..c4600a5781de 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -825,6 +825,11 @@ struct bpf_prog_pack {
unsigned long bitmap[];
};

+void bpf_jit_fill_hole_with_zero(void *area, unsigned int size)
+{
+ memset(area, 0, size);
+}
+
#define BPF_PROG_SIZE_TO_NBITS(size) (round_up(size, BPF_PROG_CHUNK_SIZE) / BPF_PROG_CHUNK_SIZE)

static DEFINE_MUTEX(pack_mutex);
@@ -864,7 +869,7 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
return pack;
}

-static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
+void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
{
unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size);
struct bpf_prog_pack *pack;
@@ -905,7 +910,7 @@ static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insn
return ptr;
}

-static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
+void bpf_prog_pack_free(struct bpf_binary_header *hdr)
{
struct bpf_prog_pack *pack = NULL, *tmp;
unsigned int nbits;
diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
index 2444bd15cc2d..fa64b80b8bca 100644
--- a/kernel/bpf/dispatcher.c
+++ b/kernel/bpf/dispatcher.c
@@ -85,12 +85,12 @@ static bool bpf_dispatcher_remove_prog(struct bpf_dispatcher *d,
return false;
}

-int __weak arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs)
+int __weak arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_funcs)
{
return -ENOTSUPP;
}

-static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image)
+static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image, void *buf)
{
s64 ips[BPF_DISPATCHER_MAX] = {}, *ipsp = &ips[0];
int i;
@@ -99,12 +99,12 @@ static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image)
if (d->progs[i].prog)
*ipsp++ = (s64)(uintptr_t)d->progs[i].prog->bpf_func;
}
- return arch_prepare_bpf_dispatcher(image, &ips[0], d->num_progs);
+ return arch_prepare_bpf_dispatcher(image, buf, &ips[0], d->num_progs);
}

static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
{
- void *old, *new;
+ void *old, *new, *tmp;
u32 noff;
int err;

@@ -117,8 +117,14 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
}

new = d->num_progs ? d->image + noff : NULL;
+ tmp = d->num_progs ? d->rw_image + noff : NULL;
if (new) {
- if (bpf_dispatcher_prepare(d, new))
+ /* Prepare the dispatcher in d->rw_image. Then use
+ * bpf_arch_text_copy to update d->image, which is RO+X.
+ */
+ if (bpf_dispatcher_prepare(d, new, tmp))
+ return;
+ if (IS_ERR(bpf_arch_text_copy(new, tmp, PAGE_SIZE / 2)))
return;
}

@@ -140,9 +146,18 @@ void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,

mutex_lock(&d->mutex);
if (!d->image) {
- d->image = bpf_jit_alloc_exec_page();
+ d->image = bpf_prog_pack_alloc(PAGE_SIZE, bpf_jit_fill_hole_with_zero);
if (!d->image)
goto out;
+ d->rw_image = bpf_jit_alloc_exec(PAGE_SIZE);
+ if (!d->rw_image) {
+ u32 size = PAGE_SIZE;
+
+ bpf_arch_text_copy(d->image, &size, sizeof(size));
+ bpf_prog_pack_free((struct bpf_binary_header *)d->image);
+ d->image = NULL;
+ goto out;
+ }
bpf_image_ksym_add(d->image, &d->ksym);
}

--
2.35.1