[PATCH v2] powerpc64/bpf: fix JIT code size calculation of bpf trampoline
Naveen N Rao
naveen at kernel.org
Sat Apr 19 21:01:15 AEST 2025
On Thu, Apr 17, 2025 at 01:10:37AM +0530, Hari Bathini wrote:
> arch_bpf_trampoline_size() provides JIT size of the BPF trampoline
> before the buffer for JIT'ing it is allocated. The total number of
> instructions emitted for BPF trampoline JIT code depends on where
> the final image is located. So, the size arrived at with the dummy
> pass in arch_bpf_trampoline_size() can vary from the actual size
> needed in arch_prepare_bpf_trampoline(). When the instructions
> accounted in arch_bpf_trampoline_size() is less than the number of
> instructions emitted during the actual JIT compile of the trampoline,
> the below warning is produced:
>
> WARNING: CPU: 8 PID: 204190 at arch/powerpc/net/bpf_jit_comp.c:981 __arch_prepare_bpf_trampoline.isra.0+0xd2c/0xdcc
>
> which is:
>
> /* Make sure the trampoline generation logic doesn't overflow */
> if (image && WARN_ON_ONCE(&image[ctx->idx] >
> (u32 *)rw_image_end - BPF_INSN_SAFETY)) {
>
> So, during the dummy pass, instead of providing some arbitrary image
> location, account for maximum possible instructions if and when there
> is a dependency with image location for JIT'ing.
>
> Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines")
> Reported-by: Venkat Rao Bagalkote <venkat88 at linux.ibm.com>
> Closes: https://lore.kernel.org/all/6168bfc8-659f-4b5a-a6fb-90a916dde3b3@linux.ibm.com/
> Cc: stable at vger.kernel.org # v6.13+
> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
> ---
>
> Changes since v1:
> - Pass NULL for image during intial pass and account for max. possible
> instruction during this pass as Naveen suggested.
>
>
> arch/powerpc/net/bpf_jit.h | 20 ++++++++++++++++---
> arch/powerpc/net/bpf_jit_comp.c | 33 ++++++++++---------------------
> arch/powerpc/net/bpf_jit_comp64.c | 9 +++++++++
> 3 files changed, 36 insertions(+), 26 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index 6beacaec63d3..4c26912c2e3c 100644
> --- a/arch/powerpc/net/bpf_jit.h
> +++ b/arch/powerpc/net/bpf_jit.h
> @@ -51,8 +51,16 @@
> EMIT(PPC_INST_BRANCH_COND | (((cond) & 0x3ff) << 16) | (offset & 0xfffc)); \
> } while (0)
>
> -/* Sign-extended 32-bit immediate load */
> +/*
> + * Sign-extended 32-bit immediate load
> + *
> + * If this is a dummy pass (!image), account for
> + * maximum possible instructions.
> + */
> #define PPC_LI32(d, i) do { \
> + if (!image) \
> + ctx->idx += 2; \
> + else { \
> if ((int)(uintptr_t)(i) >= -32768 && \
> (int)(uintptr_t)(i) < 32768) \
> EMIT(PPC_RAW_LI(d, i)); \
> @@ -60,10 +68,15 @@
> EMIT(PPC_RAW_LIS(d, IMM_H(i))); \
> if (IMM_L(i)) \
> EMIT(PPC_RAW_ORI(d, d, IMM_L(i))); \
> - } } while(0)
> + } \
> + } } while (0)
>
> #ifdef CONFIG_PPC64
> +/* If dummy pass (!image), account for maximum possible instructions */
> #define PPC_LI64(d, i) do { \
> + if (!image) \
> + ctx->idx += 5; \
> + else { \
> if ((long)(i) >= -2147483648 && \
> (long)(i) < 2147483648) \
> PPC_LI32(d, i); \
> @@ -84,7 +97,8 @@
> if ((uintptr_t)(i) & 0x000000000000ffffULL) \
> EMIT(PPC_RAW_ORI(d, d, (uintptr_t)(i) & \
> 0xffff)); \
> - } } while (0)
> + } \
> + } } while (0)
You should now also be able to remove the padding we add in
bpf_jit_comp64.c for 'case BPF_LD | BPF_IMM | BPF_DW:'
> #define PPC_LI_ADDR PPC_LI64
>
> #ifndef CONFIG_PPC_KERNEL_PCREL
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 2991bb171a9b..c0684733e9d6 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -504,10 +504,11 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
> EMIT(PPC_RAW_ADDI(_R3, _R1, regs_off));
> if (!p->jited)
> PPC_LI_ADDR(_R4, (unsigned long)p->insnsi);
> - if (!create_branch(&branch_insn, (u32 *)&ro_image[ctx->idx], (unsigned long)p->bpf_func,
> - BRANCH_SET_LINK)) {
> - if (image)
> - image[ctx->idx] = ppc_inst_val(branch_insn);
> + /* Account for max possible instructions during dummy pass for size calculation */
> + if (image && !create_branch(&branch_insn, (u32 *)&ro_image[ctx->idx],
> + (unsigned long)p->bpf_func,
> + BRANCH_SET_LINK)) {
> + image[ctx->idx] = ppc_inst_val(branch_insn);
> ctx->idx++;
> } else {
> EMIT(PPC_RAW_LL(_R12, _R25, offsetof(struct bpf_prog, bpf_func)));
> @@ -889,7 +890,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> bpf_trampoline_restore_tail_call_cnt(image, ctx, func_frame_offset, r4_off);
>
> /* Reserve space to patch branch instruction to skip fexit progs */
> - im->ip_after_call = &((u32 *)ro_image)[ctx->idx];
> + if (ro_image) /* image is NULL for dummy pass */
> + im->ip_after_call = &((u32 *)ro_image)[ctx->idx];
> EMIT(PPC_RAW_NOP());
> }
>
> @@ -912,7 +914,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> }
>
> if (flags & BPF_TRAMP_F_CALL_ORIG) {
> - im->ip_epilogue = &((u32 *)ro_image)[ctx->idx];
> + if (ro_image) /* image is NULL for dummy pass */
> + im->ip_epilogue = &((u32 *)ro_image)[ctx->idx];
> PPC_LI_ADDR(_R3, im);
> ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
> (unsigned long)__bpf_tramp_exit);
> @@ -973,25 +976,9 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> struct bpf_tramp_links *tlinks, void *func_addr)
> {
> struct bpf_tramp_image im;
> - void *image;
> int ret;
>
> - /*
> - * Allocate a temporary buffer for __arch_prepare_bpf_trampoline().
> - * This will NOT cause fragmentation in direct map, as we do not
> - * call set_memory_*() on this buffer.
> - *
> - * We cannot use kvmalloc here, because we need image to be in
> - * module memory range.
> - */
> - image = bpf_jit_alloc_exec(PAGE_SIZE);
> - if (!image)
> - return -ENOMEM;
> -
> - ret = __arch_prepare_bpf_trampoline(&im, image, image + PAGE_SIZE, image,
> - m, flags, tlinks, func_addr);
> - bpf_jit_free_exec(image);
> -
> + ret = __arch_prepare_bpf_trampoline(&im, NULL, NULL, NULL, m, flags, tlinks, func_addr);
> return ret;
> }
>
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 233703b06d7c..91f9efe8b8d7 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -225,6 +225,15 @@ int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *
> }
>
> #ifdef CONFIG_PPC_KERNEL_PCREL
> + /*
> + * If fimage is NULL (the initial pass to find image size),
> + * account for the maximum no. of instructions possible.
> + */
> + if (!fimage) {
> + ctx->idx += 7;
> + return 0;
> + }
> +
I would merge this with the below if conditional so that this gets
noticed if the instruction sequence below ever changes.
> reladdr = func_addr - local_paca->kernelbase;
>
> if (reladdr < (long)SZ_8G && reladdr >= -(long)SZ_8G) {
Other than that:
Acked-by: Naveen N Rao (AMD) <naveen at kernel.org>
- Naveen
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