Commit f42bcd16 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

bpf: teach verifier actual bounds of bpf_get_smp_processor_id() result 



bpf_get_smp_processor_id() helper returns current CPU on which BPF
program runs. It can't return value that is bigger than maximum allowed
number of CPUs (minus one, due to zero indexing). Teach BPF verifier to
recognize that. This makes it possible to use bpf_get_smp_processor_id()
result to index into arrays without extra checks, as demonstrated in
subsequent selftests/bpf patch.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230711232400.1658562-1-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 87e098e6

kernel/bpf/verifier.c

+26 −11
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <linux/btf_ids.h>

#include <linux/poison.h>

#include <linux/module.h>

#include <linux/cpumask.h>









#include "disasm.h"
















@@ -9116,19 +9117,33 @@ static void do_refine_retval_range(struct bpf_reg_state *regs, int ret_type,







{









	struct bpf_reg_state *ret_reg = &regs[BPF_REG_0];

















	if (ret_type != RET_INTEGER ||









	    (func_id != BPF_FUNC_get_stack &&









	     func_id != BPF_FUNC_get_task_stack &&









	     func_id != BPF_FUNC_probe_read_str &&









	     func_id != BPF_FUNC_probe_read_kernel_str &&









	     func_id != BPF_FUNC_probe_read_user_str))









	if (ret_type != RET_INTEGER)









		return;

















	switch (func_id) {









	case BPF_FUNC_get_stack:









	case BPF_FUNC_get_task_stack:









	case BPF_FUNC_probe_read_str:









	case BPF_FUNC_probe_read_kernel_str:









	case BPF_FUNC_probe_read_user_str:









		ret_reg->smax_value = meta->msize_max_value;









		ret_reg->s32_max_value = meta->msize_max_value;









		ret_reg->smin_value = -MAX_ERRNO;









		ret_reg->s32_min_value = -MAX_ERRNO;









		reg_bounds_sync(ret_reg);









		break;









	case BPF_FUNC_get_smp_processor_id:









		ret_reg->umax_value = nr_cpu_ids - 1;









		ret_reg->u32_max_value = nr_cpu_ids - 1;









		ret_reg->smax_value = nr_cpu_ids - 1;









		ret_reg->s32_max_value = nr_cpu_ids - 1;









		ret_reg->umin_value = 0;









		ret_reg->u32_min_value = 0;









		ret_reg->smin_value = 0;









		ret_reg->s32_min_value = 0;









		reg_bounds_sync(ret_reg);









		break;









	}









}

















static int