Le 10/11/2022 à 19:43, Hari Bathini a écrit :
> bpf_arch_text_copy is used to dump JITed binary to RX page, allowing
> multiple BPF programs to share the same page. Using patch_instruction
> to implement it.
Using patch_instruction() is nice for a quick implementation, but it is
probably suboptimal. Due to the amount of data to be copied, it is worth
a dedicated function that maps a RW copy of the page to be updated then
does the copy at once with memcpy() then unmaps the page.
>
> Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> ---
> arch/powerpc/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++++++++++++-
> 1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 43e634126514..7383e0effad2 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -13,9 +13,12 @@
> #include <linux/netdevice.h>
> #include <linux/filter.h>
> #include <linux/if_vlan.h>
> -#include <asm/kprobes.h>
> +#include <linux/memory.h>
> #include <linux/bpf.h>
>
> +#include <asm/kprobes.h>
> +#include <asm/code-patching.h>
> +
> #include "bpf_jit.h"
>
> static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
> @@ -23,6 +26,35 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
> memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
> }
>
> +/*
> + * Patch 'len' bytes of instructions from opcode to addr, one instruction
> + * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
> + */
> +static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
> +{
> + void *ret = ERR_PTR(-EINVAL);
> + size_t patched = 0;
> + u32 *inst = opcode;
> + u32 *start = addr;
> +
> + if (WARN_ON_ONCE(core_kernel_text((unsigned long)addr)))
> + return ret;
> +
> + mutex_lock(&text_mutex);
> + while (patched < len) {
> + if (patch_instruction(start++, ppc_inst(*inst)))
> + goto error;
> +
> + inst++;
> + patched += 4;
> + }
> +
> + ret = addr;
> +error:
> + mutex_unlock(&text_mutex);
> + return ret;
> +}
> +
> /* Fix updated addresses (for subprog calls, ldimm64, et al) during extra pass */
> static int bpf_jit_fixup_addresses(struct bpf_prog *fp, u32 *image,
> struct codegen_context *ctx, u32 *addrs)
> @@ -357,3 +389,8 @@ int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct code
> ctx->exentry_idx++;
> return 0;
> }
> +
> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> +{
> + return bpf_patch_instructions(dst, src, len);
> +}
I can't see the added value of having two functions when the first one
just calls the second one and is the only user of it. Why not have
implemented bpf_patch_instructions() directly inside bpf_arch_text_copy() ?
By the way, it can be nice to have two functions, but split them
differently, to avoid the goto: etc ....
I also prefer using for loops instead of while loops.
It could have looked like below (untested):
static void *bpf_patch_instructions(void *addr, void *opcode, size_t len)
{
u32 *inst = opcode;
u32 *start = addr;
u32 *end = addr + len;
for (inst = opcode, start = addr; start < end; inst++, start++) {
if (patch_instruction(start, ppc_inst(*inst)))
return ERR_PTR(-EINVAL);
}
return addr;
}
void *bpf_arch_text_copy(void *dst, void *src, size_t len)
{
if (WARN_ON_ONCE(core_kernel_text((unsigned long)dst)))
return ret;
mutex_lock(&text_mutex);
ret = bpf_patch_instructions(dst, src, len);
mutex_unlock(&text_mutex);
return ret;
}
