Re: [PATCH bpf-next v2 3/3] bpf, riscv: use prog pack allocator in the BPF JIT
From: Pu Lehui
Date: Fri Aug 25 2023 - 21:37:13 EST
On 2023/8/25 19:40, Puranjay Mohan wrote:
Hi Pu,
On Fri, Aug 25, 2023 at 1:12 PM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
On 2023/8/25 16:42, Puranjay Mohan wrote:
Hi Pu,
On Fri, Aug 25, 2023 at 9:34 AM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
On 2023/8/25 15:09, Pu Lehui wrote:
Hi Puranjay,
Happy to see the RV64 pack allocator implementation.
RV32 also
On 2023/8/24 21:31, Puranjay Mohan wrote:
Use bpf_jit_binary_pack_alloc() for memory management of JIT binaries in
RISCV BPF JIT. The bpf_jit_binary_pack_alloc creates a pair of RW and RX
buffers. The JIT writes the program into the RW buffer. When the JIT is
done, the program is copied to the final RX buffer with
bpf_jit_binary_pack_finalize.
Implement bpf_arch_text_copy() and bpf_arch_text_invalidate() for RISCV
JIT as these functions are required by bpf_jit_binary_pack allocator.
Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
---
arch/riscv/net/bpf_jit.h | 3 +
arch/riscv/net/bpf_jit_comp64.c | 56 +++++++++++++---
arch/riscv/net/bpf_jit_core.c | 113 +++++++++++++++++++++++++++-----
3 files changed, 146 insertions(+), 26 deletions(-)
diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index 2717f5490428..ad69319c8ea7 100644
--- a/arch/riscv/net/bpf_jit.h
+++ b/arch/riscv/net/bpf_jit.h
@@ -68,6 +68,7 @@ static inline bool is_creg(u8 reg)
struct rv_jit_context {
struct bpf_prog *prog;
u16 *insns; /* RV insns */
+ u16 *ro_insns;
In fact, the definition of w/ or w/o ro_ still looks a bit confusing.
Maybe it is better for us not to change the current framework, as the
current `image` is the final executed RX image, and the trampoline
treats `image` as the same. Maybe it would be better to add a new RW
image, such like `rw_iamge`, so that we do not break the existing
framework and do not have to add too many comments.
I had thought about this and decided to create a new _ro image/header
and not _rw image/header. Here is my reasoning:
If we let the existing insns, header be considered the read_only
version from where the
program will run, and create new rw_insn and rw_header for doing the jit process
it would require a lot more changes to the framework.
functions like build_body(), bpf_jit_build_prologue(), etc. work on
ctx->insns and
Hmm, the other parts should be fine, but the emit instruction is a
problem. All right, let's go ahead.
now all these references would have to be changed to ctx->rw_insns.
Howsoever we implement this, there is no way to do it without changing
the current framework.
The crux of the problem is that we need to use the r/w area for
writing and the r/x area for calculating
offsets.
If you think this can be done in a more efficient way then I would
love to implement that, but all other
solutions that I tried made the code very difficult to follow.
And any other parts, it looks great.😄
int ninsns;
int prologue_len;
int epilogue_offset;
@@ -85,7 +86,9 @@ static inline int ninsns_rvoff(int ninsns)
struct rv_jit_data {
struct bpf_binary_header *header;
+ struct bpf_binary_header *ro_header;
u8 *image;
+ u8 *ro_image;
struct rv_jit_context ctx;
};
diff --git a/arch/riscv/net/bpf_jit_comp64.c
b/arch/riscv/net/bpf_jit_comp64.c
index 0ca4f5c0097c..d77b16338ba2 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -144,7 +144,11 @@ static bool in_auipc_jalr_range(s64 val)
/* Emit fixed-length instructions for address */
static int emit_addr(u8 rd, u64 addr, bool extra_pass, struct
rv_jit_context *ctx)
{
- u64 ip = (u64)(ctx->insns + ctx->ninsns);
+ /*
+ * Use the ro_insns(RX) to calculate the offset as the BPF
program will
+ * finally run from this memory region.
+ */
+ u64 ip = (u64)(ctx->ro_insns + ctx->ninsns);
s64 off = addr - ip;
s64 upper = (off + (1 << 11)) >> 12;
s64 lower = off & 0xfff;
@@ -465,7 +469,11 @@ static int emit_call(u64 addr, bool fixed_addr,
struct rv_jit_context *ctx)
u64 ip;
if (addr && ctx->insns) {
ctx->insns need to sync to ctx->ro_insns
Can you elaborate this more. I am missing something here.
The sync happens at the end by calling bpf_jit_binary_pack_finalize().
if (addr && ctx->insns) {
ip = (u64)(long)(ctx->ro_insns + ctx->ninsns);
off = addr - ip;
}
emit ctx->insns + off
Here we are assuming ctx->insns == ctx->ro_insns, if they not, the
offset calculated by ctx->ro_insns will not meaningful for ctx->insns.
We are not assuming that ctx->insns == ctx->ro_insns at this point.
We are just finding the offset: off = addr(let's say in kernel) -
ip(address of the instruction);
I was curious why we need to use ro_insns to calculate offset? Is that
any problem if we do jit iteration with ctx->insns and the final copy
ctx->insns to ro_insns?
All the offsets within the image can be calculated using ctx->insns and it will
work but if the emit_call() is for an address in the kernel code let's
say, then the
offset between this address(in kernel) and the R/W image would be different from
the offset between the address(in kernel) and the R/O image.
We need the offset between the R/X Image and the kernel address. Because the
CPU will execute the instructions from there.
Agree with that, thanks for explaination. Let's talk about my original
idea, shall we add check like this to reject ctx->ro_insns == NULL?
if (addr && ctx->insns && ctx->ro_insns) {
...
}
- ip = (u64)(long)(ctx->insns + ctx->ninsns);
+ /*
+ * Use the ro_insns(RX) to calculate the offset as the BPF
+ * program will finally run from this memory region.
+ */
+ ip = (u64)(long)(ctx->ro_insns + ctx->ninsns);
off = addr - ip;
}
@@ -578,7 +586,8 @@ static int add_exception_handler(const struct
bpf_insn *insn,
{
struct exception_table_entry *ex;
unsigned long pc;
- off_t offset;
+ off_t ins_offset;
+ off_t fixup_offset;
if (!ctx->insns || !ctx->prog->aux->extable ||
BPF_MODE(insn->code) != BPF_PROBE_MEM)
ctx->ro_insns need to be checked also.
ctx->ro_insns is not initialised until we call bpf_jit_binary_pack_finalize()?
ctx->ro_insns and ctx->insns are both allocated together by
bpf_jit_binary_pack_alloc().
ctx->ro_insns is marked R/X and ctx->insns is marked R/W. We dump all
instructions in
ctx->insns and then copy them to ctx->ro_insns with
bpf_jit_binary_pack_finalize().
The catch is that instructions that work with offsets like JAL need
the offsets from ctx->ro_insns.
as explained above.
if (!ctx->insns || !ctx->prog->aux->extable ||
...
pc = (unsigned long)&ctx->ro_insns[ctx->ninsns - insn_len];
Also here, to add check like this to reject ctx->ro_insns == NULL which
may cause null pointer dereference?
if (!ctx->insns || !ctx->ro_insns || !ctx->prog->aux->extable ||
The uninitialized ctx->ro_insns may lead to illegal address access.
Although it will never happen, because we also assume that ctx->insns ==
ctx->ro_insns.
Here also we are not assuming ctx->insns == ctx->ro_insns. The ctx->ro_insns is
allocated but not initialised yet. So all addresses in range
ctx->ro_insns to ctx->ro_insns + size
are valid addresses. Here we are using the addresses only to find the
offset and not accessing those
addresses.
return 0;
@@ -593,12 +602,17 @@ static int add_exception_handler(const struct
bpf_insn *insn,
return -EINVAL;
ex = &ctx->prog->aux->extable[ctx->nexentries];
- pc = (unsigned long)&ctx->insns[ctx->ninsns - insn_len];
+ pc = (unsigned long)&ctx->ro_insns[ctx->ninsns - insn_len];
- offset = pc - (long)&ex->insn;
- if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN))
+ /*
+ * This is the relative offset of the instruction that may fault
from
+ * the exception table itself. This will be written to the exception
+ * table and if this instruction faults, the destination register
will
+ * be set to '0' and the execution will jump to the next
instruction.
+ */
+ ins_offset = pc - (long)&ex->insn;
+ if (WARN_ON_ONCE(ins_offset >= 0 || ins_offset < INT_MIN))
return -ERANGE;
- ex->insn = offset;
/*
* Since the extable follows the program, the fixup offset is
always
@@ -607,12 +621,25 @@ static int add_exception_handler(const struct
bpf_insn *insn,
* bits. We don't need to worry about buildtime or runtime sort
* modifying the upper bits because the table is already sorted,
and
* isn't part of the main exception table.
+ *
+ * The fixup_offset is set to the next instruction from the
instruction
+ * that may fault. The execution will jump to this after handling
the
+ * fault.
*/
- offset = (long)&ex->fixup - (pc + insn_len * sizeof(u16));
- if (!FIELD_FIT(BPF_FIXUP_OFFSET_MASK, offset))
+ fixup_offset = (long)&ex->fixup - (pc + insn_len * sizeof(u16));
+ if (!FIELD_FIT(BPF_FIXUP_OFFSET_MASK, fixup_offset))
return -ERANGE;
- ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, offset) |
+ /*
+ * The offsets above have been calculated using the RO buffer but we
+ * need to use the R/W buffer for writes.
+ * switch ex to rw buffer for writing.
+ */
+ ex = (void *)ctx->insns + ((void *)ex - (void *)ctx->ro_insns);
+
+ ex->insn = ins_offset;
+
+ ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, fixup_offset) |
FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg);
ex->type = EX_TYPE_BPF;
@@ -1006,6 +1033,7 @@ int arch_prepare_bpf_trampoline(struct
bpf_tramp_image *im, void *image,
ctx.ninsns = 0;
ctx.insns = NULL;
+ ctx.ro_insns = NULL;
ret = __arch_prepare_bpf_trampoline(im, m, tlinks, func_addr,
flags, &ctx);
if (ret < 0)
return ret;
@@ -1014,7 +1042,15 @@ int arch_prepare_bpf_trampoline(struct
bpf_tramp_image *im, void *image,
return -EFBIG;
ctx.ninsns = 0;
+ /*
+ * The bpf_int_jit_compile() uses a RW buffer (ctx.insns) to
write the
+ * JITed instructions and later copies it to a RX region
(ctx.ro_insns).
+ * It also uses ctx.ro_insns to calculate offsets for jumps etc.
As the
+ * trampoline image uses the same memory area for writing and
execution,
+ * both ctx.insns and ctx.ro_insns can be set to image.
+ */
ctx.insns = image;
+ ctx.ro_insns = image;
ret = __arch_prepare_bpf_trampoline(im, m, tlinks, func_addr,
flags, &ctx);
if (ret < 0)
return ret;
diff --git a/arch/riscv/net/bpf_jit_core.c
b/arch/riscv/net/bpf_jit_core.c
index 7a26a3e1c73c..4c8dffc09368 100644
--- a/arch/riscv/net/bpf_jit_core.c
+++ b/arch/riscv/net/bpf_jit_core.c
@@ -8,6 +8,8 @@
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/memory.h>
+#include <asm/patch.h>
#include "bpf_jit.h"
/* Number of iterations to try until offsets converge. */
@@ -117,16 +119,27 @@ struct bpf_prog *bpf_int_jit_compile(struct
bpf_prog *prog)
sizeof(struct exception_table_entry);
prog_size = sizeof(*ctx->insns) * ctx->ninsns;
- jit_data->header =
- bpf_jit_binary_alloc(prog_size + extable_size,
- &jit_data->image,
- sizeof(u32),
- bpf_fill_ill_insns);
- if (!jit_data->header) {
+ jit_data->ro_header =
+ bpf_jit_binary_pack_alloc(prog_size +
+ extable_size,
+ &jit_data->ro_image,
+ sizeof(u32),
+ &jit_data->header,
+ &jit_data->image,
+ bpf_fill_ill_insns);
+ if (!jit_data->ro_header) {
prog = orig_prog;
goto out_offset;
}
+ /*
+ * Use the image(RW) for writing the JITed instructions.
But also save
+ * the ro_image(RX) for calculating the offsets in the
image. The RW
+ * image will be later copied to the RX image from where
the program
+ * will run. The bpf_jit_binary_pack_finalize() will do
this copy in the
+ * final step.
+ */
+ ctx->ro_insns = (u16 *)jit_data->ro_image;
ctx->insns = (u16 *)jit_data->image;
/*
* Now, when the image is allocated, the image can
@@ -138,14 +151,12 @@ struct bpf_prog *bpf_int_jit_compile(struct
bpf_prog *prog)
if (i == NR_JIT_ITERATIONS) {
pr_err("bpf-jit: image did not converge in <%d passes!\n", i);
- if (jit_data->header)
- bpf_jit_binary_free(jit_data->header);
prog = orig_prog;
- goto out_offset;
+ goto out_free_hdr;
}
if (extable_size)
- prog->aux->extable = (void *)ctx->insns + prog_size;
+ prog->aux->extable = (void *)ctx->ro_insns + prog_size;
skip_init_ctx:
pass++;
@@ -154,23 +165,35 @@ struct bpf_prog *bpf_int_jit_compile(struct
bpf_prog *prog)
bpf_jit_build_prologue(ctx);
if (build_body(ctx, extra_pass, NULL)) {
- bpf_jit_binary_free(jit_data->header);
prog = orig_prog;
- goto out_offset;
+ goto out_free_hdr;
}
bpf_jit_build_epilogue(ctx);
if (bpf_jit_enable > 1)
bpf_jit_dump(prog->len, prog_size, pass, ctx->insns);
- prog->bpf_func = (void *)ctx->insns;
+ prog->bpf_func = (void *)ctx->ro_insns;
prog->jited = 1;
prog->jited_len = prog_size;
- bpf_flush_icache(jit_data->header, ctx->insns + ctx->ninsns);
-
if (!prog->is_func || extra_pass) {
- bpf_jit_binary_lock_ro(jit_data->header);
+ if (WARN_ON(bpf_jit_binary_pack_finalize(prog,
+ jit_data->ro_header,
+ jit_data->header))) {
+ /* ro_header has been freed */
+ jit_data->ro_header = NULL;
+ prog = orig_prog;
+ goto out_offset;
+ }
+ /*
+ * The instructions have now been copied to the ROX region from
+ * where they will execute.
+ * Write any modified data cache blocks out to memory and
+ * invalidate the corresponding blocks in the instruction cache.
+ */
+ bpf_flush_icache(jit_data->ro_header,
+ ctx->ro_insns + ctx->ninsns);
for (i = 0; i < prog->len; i++)
ctx->offset[i] = ninsns_rvoff(ctx->offset[i]);
bpf_prog_fill_jited_linfo(prog, ctx->offset);
@@ -185,6 +208,15 @@ struct bpf_prog *bpf_int_jit_compile(struct
bpf_prog *prog)
bpf_jit_prog_release_other(prog, prog == orig_prog ?
tmp : orig_prog);
return prog;
+
+out_free_hdr:
+ if (jit_data->header) {
+ bpf_arch_text_copy(&jit_data->ro_header->size,
+ &jit_data->header->size,
+ sizeof(jit_data->header->size));
+ bpf_jit_binary_pack_free(jit_data->ro_header, jit_data->header);
+ }
+ goto out_offset;
}
u64 bpf_jit_alloc_exec_limit(void)
@@ -204,3 +236,52 @@ void bpf_jit_free_exec(void *addr)
{
return vfree(addr);
}
+
+void *bpf_arch_text_copy(void *dst, void *src, size_t len)
+{
+ int ret;
+
+ mutex_lock(&text_mutex);
+ ret = patch_text_nosync(dst, src, len);
+ mutex_unlock(&text_mutex);
+
+ if (ret)
+ return ERR_PTR(-EINVAL);
+
+ return dst;
+}
+
+int bpf_arch_text_invalidate(void *dst, size_t len)
+{
+ int ret = 0;
no need to initialize it
+
+ mutex_lock(&text_mutex);
+ ret = patch_text_set_nosync(dst, 0, len);
+ mutex_unlock(&text_mutex);
+
+ return ret;
+}
+
+void bpf_jit_free(struct bpf_prog *prog)
+{
+ if (prog->jited) {
+ struct rv_jit_data *jit_data = prog->aux->jit_data;
+ struct bpf_binary_header *hdr;
+
+ /*
+ * If we fail the final pass of JIT (from jit_subprogs),
+ * the program may not be finalized yet. Call finalize here
+ * before freeing it.
+ */
+ if (jit_data) {
+ bpf_jit_binary_pack_finalize(prog, jit_data->ro_header,
+ jit_data->header);
+ kfree(jit_data);
+ }
+ hdr = bpf_jit_binary_pack_hdr(prog);
+ bpf_jit_binary_pack_free(hdr, NULL);
+ WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(prog));
+ }
+
+ bpf_prog_unlock_free(prog);
+}
Thanks,
Puranjay
Thanks,
Puranjay