Re: [PATCH bpf-next v2 3/3] bpf, riscv: use prog pack allocator in the BPF JIT

Pu Lehui
2023-08-25T11:12:52Z

On 2023/8/25 16:42, Puranjay Mohan wrote:
> Hi Pu,
>
> On Fri, Aug 25, 2023 at 9:34 AM Pu Lehui <pulehui@huawei.com> 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@gmail.com>
>>>> ---
>>>> 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.
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?

>
>>>
>>>> - 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()?

if (!ctx->insns || !ctx->prog->aux->extable ||
...
pc = (unsigned long)&ctx->ro_insns[ctx->ninsns - insn_len];

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.

>
>>>
>>>> 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