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Subject[RFC PATCH bpf-next 3/4] riscv, bpf: Add bpf_arch_text_poke support for RV64
Date
From: Pu Lehui <pulehui@huawei.com>

Implement bpf_arch_text_poke for RV64. For call scenario,
ftrace framework reserve 4 nops for RV64 kernel function
as function entry, and use auipc+jalr instructions to call
kernel or module functions. However, since the auipc+jalr
call instructions is non-atomic operation, we need to use
stop-machine to make sure instruction patching in atomic
context. As for jump scenario, since we only jump inside
the trampoline, a jal instruction is sufficient.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
arch/riscv/net/bpf_jit.h | 5 ++
arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
2 files changed, 134 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index d926e0f7ef57..bf9802a63061 100644
--- a/arch/riscv/net/bpf_jit.h
+++ b/arch/riscv/net/bpf_jit.h
@@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
}

+static inline u32 rv_nop(void)
+{
+ return rv_i_insn(0, 0, 0, 0, 0x13);
+}
+
/* RVC instrutions. */

static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index bf4721a99a09..fa8b03c52463 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -8,6 +8,8 @@
#include <linux/bitfield.h>
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/memory.h>
+#include <linux/stop_machine.h>
#include "bpf_jit.h"

#define RV_REG_TCC RV_REG_A6
@@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
if (!is_tail_call)
emit_mv(RV_REG_A0, RV_REG_A5, ctx);
emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
- is_tail_call ? 4 : 0, /* skip TCC init */
+ is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
ctx);
}

@@ -615,6 +617,127 @@ static int add_exception_handler(const struct bpf_insn *insn,
return 0;
}

+struct text_poke_args {
+ void *addr;
+ const void *insns;
+ size_t len;
+ atomic_t cpu_count;
+};
+
+static int do_text_poke(void *data)
+{
+ int ret = 0;
+ struct text_poke_args *patch = data;
+
+ if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
+ ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
+ atomic_inc(&patch->cpu_count);
+ } else {
+ while (atomic_read(&patch->cpu_count) <= num_online_cpus())
+ cpu_relax();
+ smp_mb();
+ }
+
+ return ret;
+}
+
+static int bpf_text_poke_stop_machine(void *addr, const void *insns, size_t len)
+{
+ struct text_poke_args patch = {
+ .addr = addr,
+ .insns = insns,
+ .len = len,
+ .cpu_count = ATOMIC_INIT(0),
+ };
+
+ return stop_machine(do_text_poke, &patch, cpu_online_mask);
+}
+
+static int gen_call_or_nops(void *target, void *ip, u32 *insns)
+{
+ int i, ret;
+ s64 rvoff;
+ struct rv_jit_context ctx;
+
+ ctx.ninsns = 0;
+ ctx.insns = (u16 *)insns;
+
+ if (!target) {
+ for (i = 0; i < 4; i++)
+ emit(rv_nop(), &ctx);
+ return 0;
+ }
+
+ rvoff = (s64)(target - ip);
+ emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
+ ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
+ if (ret)
+ return ret;
+ emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
+
+ return 0;
+
+}
+
+static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
+{
+ int ret;
+ u32 old_insns[4], new_insns[4];
+
+ ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
+ if (ret)
+ return ret;
+
+ ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
+ if (ret)
+ return ret;
+
+ mutex_lock(&text_mutex);
+ if (memcmp(ip, old_insns, sizeof(old_insns))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (memcmp(ip, new_insns, sizeof(new_insns)))
+ ret = bpf_text_poke_stop_machine(ip, new_insns, sizeof(new_insns));
+out:
+ mutex_unlock(&text_mutex);
+ return ret;
+}
+
+static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
+{
+ int ret;
+ u32 old_insn, new_insn;
+
+ old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >> 1) : rv_nop();
+ new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >> 1) : rv_nop();
+
+ mutex_lock(&text_mutex);
+ if (memcmp(ip, &old_insn, sizeof(old_insn))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (memcmp(ip, &new_insn, sizeof(new_insn)))
+ ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
+out:
+ mutex_unlock(&text_mutex);
+ return ret;
+}
+
+int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
+ void *old_addr, void *new_addr)
+{
+ if (!is_kernel_text((unsigned long)ip) &&
+ !is_bpf_text_address((unsigned long)ip))
+ return -ENOTSUPP;
+
+ return poke_type == BPF_MOD_CALL ?
+ bpf_text_poke_call(ip, old_addr, new_addr) :
+ bpf_text_poke_jump(ip, old_addr, new_addr);
+}
+
int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
bool extra_pass)
{
@@ -1266,7 +1389,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,

void bpf_jit_build_prologue(struct rv_jit_context *ctx)
{
- int stack_adjust = 0, store_offset, bpf_stack_adjust;
+ int i, stack_adjust = 0, store_offset, bpf_stack_adjust;
bool is_main_prog = ctx->prog->aux->func_idx == 0;

bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
@@ -1294,6 +1417,10 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx)

store_offset = stack_adjust - 8;

+ /* reserve 4 nop insns */
+ for (i = 0; i < 4; i++)
+ emit(rv_nop(), ctx);
+
/* First instruction is always setting the tail-call-counter
* (TCC) register. This instruction is skipped for tail calls.
* Force using a 4-byte (non-compressed) instruction.
--
2.25.1
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