On 3/4/22 11:16 AM, Hao Luo wrote:
With the introduction of MEM_USER in
commit c6f1bfe89ac9 ("bpf: reject program if a __user tagged memory accessed in kernel way")
PTR_TO_BTF_ID can be combined with a MEM_USER tag. Therefore, most
likely, when we compare reg_type against PTR_TO_BTF_ID, we want to use
the reg's base_type. Previously the check in check_mem_access() wants
to say: if the reg is BTF_ID but not NULL, the execution flow falls
into the 'then' branch. But now a reg of (BTF_ID | MEM_USER), which
should go into the 'then' branch, goes into the 'else'.
The end results before and after this patch are the same: regs tagged
with MEM_USER get rejected, but not in a way we intended. So fix the
condition, the error message now is correct.
Before (log from commit 696c39011538):
$ ./test_progs -v -n 22/3
...
libbpf: prog 'test_user1': BPF program load failed: Permission denied
libbpf: prog 'test_user1': -- BEGIN PROG LOAD LOG --
R1 type=ctx expected=fp
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
; int BPF_PROG(test_user1, struct bpf_testmod_btf_type_tag_1 *arg)
0: (79) r1 = *(u64 *)(r1 +0)
func 'bpf_testmod_test_btf_type_tag_user_1' arg0 has btf_id 136561 type STRUCT 'bpf_testmod_btf_type_tag_1'
1: R1_w=user_ptr_bpf_testmod_btf_type_tag_1(id=0,off=0,imm=0)
; g = arg->a;
1: (61) r1 = *(u32 *)(r1 +0)
R1 invalid mem access 'user_ptr_'
Now:
libbpf: prog 'test_user1': BPF program load failed: Permission denied
libbpf: prog 'test_user1': -- BEGIN PROG LOAD LOG --
R1 type=ctx expected=fp
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
; int BPF_PROG(test_user1, struct bpf_testmod_btf_type_tag_1 *arg)
0: (79) r1 = *(u64 *)(r1 +0)
func 'bpf_testmod_test_btf_type_tag_user_1' arg0 has btf_id 104036 type STRUCT 'bpf_testmod_btf_type_tag_1'
1: R1_w=user_ptr_bpf_testmod_btf_type_tag_1(id=0,ref_obj_id=0,off=0,imm=0)
; g = arg->a;
1: (61) r1 = *(u32 *)(r1 +0)
R1 is ptr_bpf_testmod_btf_type_tag_1 access user memory: off=0
Note the error message for the reason of rejection.
Fixes: c6f1bfe89ac9 ("bpf: reject program if a __user tagged memory accessed in kernel way")
Cc: Yonghong Song <yhs@xxxxxx>
Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
Thanks for the fix!
Acked-by: Yonghong Song <yhs@xxxxxx>
