> On Nov 6, 2019, at 9:46 PM, Alexei Starovoitov <ast@xxxxxxxxxx> wrote:
>
> Add bpf_arch_text_poke() helper that is used by BPF trampoline logic to patch
> nops/calls in kernel text into calls into BPF trampoline and to patch
> calls/nops inside BPF programs too.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 51 +++++++++++++++++++++++++++++++++++++
> include/linux/bpf.h | 8 ++++++
> kernel/bpf/core.c | 6 +++++
> 3 files changed, 65 insertions(+)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 0399b1f83c23..8631d3bd637f 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -9,9 +9,11 @@
> #include <linux/filter.h>
> #include <linux/if_vlan.h>
> #include <linux/bpf.h>
> +#include <linux/memory.h>
> #include <asm/extable.h>
> #include <asm/set_memory.h>
> #include <asm/nospec-branch.h>
> +#include <asm/text-patching.h>
>
> static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
> {
> @@ -487,6 +489,55 @@ static int emit_call(u8 **pprog, void *func, void *ip)
> return 0;
> }
>
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> + void *old_addr, void *new_addr)
> +{
> + u8 old_insn[NOP_ATOMIC5] = {};
> + u8 new_insn[NOP_ATOMIC5] = {};
> + u8 *prog;
> + int ret;
> +
> + if (!is_kernel_text((long)ip))
> + /* BPF trampoline in modules is not supported */
> + return -EINVAL;
> +
> + if (old_addr) {
> + prog = old_insn;
> + ret = emit_call(&prog, old_addr, (void *)ip);
> + if (ret)
> + return ret;
> + }
> + if (old_addr) {
^ should be new_addr?
> + prog = new_insn;
> + ret = emit_call(&prog, old_addr, (void *)ip);
^^^ and here?
> + if (ret)
> + return ret;
> + }
> + ret = -EBUSY;
> + mutex_lock(&text_mutex);
> + switch (t) {
> + case BPF_MOD_NOP_TO_CALL:
> + if (memcmp(ip, ideal_nops, 5))
Maybe use X86_CALL_SIZE instead of 5? And the five more "5" below?
> + goto out;
> + text_poke(ip, new_insn, 5);
> + break;
> + case BPF_MOD_CALL_TO_CALL:
> + if (memcmp(ip, old_insn, 5))
> + goto out;
> + text_poke(ip, new_insn, 5);
> + break;
> + case BPF_MOD_CALL_TO_NOP:
> + if (memcmp(ip, old_insn, 5))
> + goto out;
> + text_poke(ip, ideal_nops, 5);
> + break;
> + }
> + ret = 0;
> +out:
> + mutex_unlock(&text_mutex);
> + return ret;
> +}
> +
> static bool ex_handler_bpf(const struct exception_table_entry *x,
> struct pt_regs *regs, int trapnr,
> unsigned long error_code, unsigned long fault_addr)
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 7c7f518811a6..8b90db25348a 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1157,4 +1157,12 @@ static inline u32 bpf_xdp_sock_convert_ctx_access(enum bpf_access_type type,
> }
> #endif /* CONFIG_INET */
>
> +enum bpf_text_poke_type {
> + BPF_MOD_NOP_TO_CALL,
> + BPF_MOD_CALL_TO_CALL,
> + BPF_MOD_CALL_TO_NOP,
> +};
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> + void *addr1, void *addr2);
> +
> #endif /* _LINUX_BPF_H */
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 97e37d82a1cc..856564e97943 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2140,6 +2140,12 @@ int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
> return -EFAULT;
> }
>
> +int __weak bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> + void *addr1, void *addr2)
> +{
> + return -ENOTSUPP;
> +}
> +
> DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
> EXPORT_SYMBOL(bpf_stats_enabled_key);
>
> --
> 2.23.0
>
