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

Puranjay Mohan
2023-08-25T11:40:51Z

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.

>
> >
> >>>
> >>>> - 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];
>
> 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