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

Pu Lehui
2023-08-26T01:36:23Z

On 2023/8/25 19:40, Puranjay Mohan wrote:
> Hi Pu,
>
> On Fri, Aug 25, 2023 at 1:12 PM Pu Lehui <pulehui@huawei.com> wrote:
>>
>>
>>
>> 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.
>
> 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