From 9b9f0b42703ceb88332bcb19453c4288c2683e34 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 22 Apr 2026 20:35:01 -0700 Subject: bpf: Prepare verifier logs for upcoming kfunc stack arguments This change prepares verifier log reporting for upcoming kfunc stack argument support. Currently verifier log code mostly assumes that an argument can be described directly by a register number. That works for arguments passed in `R1` to `R5`, but it does not work once kfunc arguments can also be passed on the stack. Introduce an opaque `argno_t` type that encodes both register-based and arg-based references. Four helpers form the interface: - argno_from_reg(regno): create from a register number - argno_from_arg(arg): create from a 1-based arg number - reg_from_argno(a): extract register number, or -1 - arg_from_argno(a): extract arg number, or -1 reg_arg_name() converts an argno_t to a human-readable string for verifier logs: "R%d" for register arguments, or "*(R11-off)" for stack arguments beyond R5. Update selftests accordingly. Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20260423033501.2539667-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- include/linux/bpf_verifier.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index b148f816f25b..d5b4303315dd 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -913,6 +913,7 @@ struct bpf_verifier_env { * e.g., in reg_type_str() to generate reg_type string */ char tmp_str_buf[TMP_STR_BUF_LEN]; + char tmp_arg_name[32]; struct bpf_insn insn_buf[INSN_BUF_SIZE]; struct bpf_insn epilogue_buf[INSN_BUF_SIZE]; struct bpf_scc_callchain callchain_buf; -- cgit v1.2.3 From 246ad6e5ee259669692bdb7fb353e8c5d5bba628 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 22 Apr 2026 20:35:06 -0700 Subject: bpf: Introduce bpf register BPF_REG_PARAMS Introduce BPF_REG_PARAMS as a dedicated BPF register for stack argument accesses. It occupies the BPF register number 11 (R11), which is used as the base pointer for the stack argument area, keeping it separate from the R10-based (BPF_REG_FP) program stack. The kernel-internal hidden register BPF_REG_AX previously occupied slot 11 (MAX_BPF_REG). With BPF_REG_PARAMS taking that slot, BPF_REG_AX moves to slot 12 and MAX_BPF_EXT_REG increases accordingly. Acked-by: Puranjay Mohan Acked-by: Kumar Kartikeya Dwivedi Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20260423033506.2542005-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- include/linux/filter.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/filter.h b/include/linux/filter.h index 1ec6d5ba64cc..b77d0b06db6e 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -58,8 +58,9 @@ struct ctl_table_header; #define BPF_REG_H BPF_REG_9 /* hlen, callee-saved */ /* Kernel hidden auxiliary/helper register. */ -#define BPF_REG_AX MAX_BPF_REG -#define MAX_BPF_EXT_REG (MAX_BPF_REG + 1) +#define BPF_REG_PARAMS MAX_BPF_REG +#define BPF_REG_AX (MAX_BPF_REG + 1) +#define MAX_BPF_EXT_REG (MAX_BPF_REG + 2) #define MAX_BPF_JIT_REG MAX_BPF_EXT_REG /* unused opcode to mark special call to bpf_tail_call() helper */ -- cgit v1.2.3 From 4439328d3878c97fdf5ddec828a43ea07c388452 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 22 Apr 2026 20:35:11 -0700 Subject: bpf: Reuse MAX_BPF_FUNC_ARGS for maximum number of arguments Currently, MAX_BPF_FUNC_ARGS is used for tracepoint related progs where the number of parameters cannot exceed MAX_BPF_FUNC_ARGS. Here, MAX_BPF_FUNC_ARGS is reused to set a limit of the number of arguments for bpf functions and kfuncs. The current value for MAX_BPF_FUNC_ARGS is 12 which should be sufficient for majority of bpf functions and kfuncs. Acked-by: Puranjay Mohan Acked-by: Kumar Kartikeya Dwivedi Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20260423033511.2542870-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index d3aea3931b85..715b6df9c403 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1151,6 +1151,11 @@ struct bpf_prog_offload { /* The longest tracepoint has 12 args. * See include/trace/bpf_probe.h + * + * Also reuse this macro for maximum number of arguments a BPF function + * or a kfunc can have. Args 1-5 are passed in registers, args 6-12 via + * stack arg slots. The JIT may map some stack arg slots to registers based + * on the native calling convention (e.g., arg 6 to R9 on x86-64). */ #define MAX_BPF_FUNC_ARGS 12 -- cgit v1.2.3