[bpf-next,v2,6/7] selftests/bpf: Avoid load failure for token_lsm.c

Commit Message

Xu Kuohai March 25, 2024, 9:56 a.m. UTC

From: Xu Kuohai <[e-mail]>

The compiler optimized the two bpf progs in token_lsm.c to make return
value from the bool variable in the "return -1" path, causing an
unexpected rejection:

0: R1=ctx() R10=fp0
; int BPF_PROG(bpf_token_capable, struct bpf_token *token, int cap) @ bpf_lsm.c:17
0: (b7) r6 = 0                        ; R6_w=0
; if (my_pid == 0 || my_pid != (bpf_get_current_pid_tgid() >> 32)) @ bpf_lsm.c:19
1: (18) r1 = 0xffffc9000102a000       ; R1_w=map_value(map=bpf_lsm.bss,ks=4,vs=5)
3: (61) r7 = *(u32 *)(r1 +0)          ; R1_w=map_value(map=bpf_lsm.bss,ks=4,vs=5) R7_w=scalar(smin=0,smax=umax=0xffffffff,var_off=(0x0; 0xffffffff))
4: (15) if r7 == 0x0 goto pc+11       ; R7_w=scalar(smin=umin=umin32=1,smax=umax=0xffffffff,var_off=(0x0; 0xffffffff))
5: (67) r7 <<= 32                     ; R7_w=scalar(smax=0x7fffffff00000000,umax=0xffffffff00000000,smin32=0,smax32=umax32=0,var_off=(0x0; 0xffffffff00000000))
6: (c7) r7 s>>= 32                    ; R7_w=scalar(smin=0xffffffff80000000,smax=0x7fffffff)
7: (85) call bpf_get_current_pid_tgid#14      ; R0=scalar()
8: (77) r0 >>= 32                     ; R0_w=scalar(smin=0,smax=umax=0xffffffff,var_off=(0x0; 0xffffffff))
9: (5d) if r0 != r7 goto pc+6         ; R0_w=scalar(smin=smin32=0,smax=umax=umax32=0x7fffffff,var_off=(0x0; 0x7fffffff)) R7=scalar(smin=smin32=0,smax=umax=umax32=0x7fffffff,var_off=(0x0; 0x7fffffff))
; if (reject_capable) @ bpf_lsm.c:21
10: (18) r1 = 0xffffc9000102a004      ; R1_w=map_value(map=bpf_lsm.bss,ks=4,vs=5,off=4)
12: (71) r6 = *(u8 *)(r1 +0)          ; R1_w=map_value(map=bpf_lsm.bss,ks=4,vs=5,off=4) R6_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff))
;  @ bpf_lsm.c:0
13: (87) r6 = -r6                     ; R6_w=scalar()
14: (67) r6 <<= 56                    ; R6_w=scalar(smax=0x7f00000000000000,umax=0xff00000000000000,smin32=0,smax32=umax32=0,var_off=(0x0; 0xff00000000000000))
15: (c7) r6 s>>= 56                   ; R6_w=scalar(smin=smin32=-128,smax=smax32=127)
; int BPF_PROG(bpf_token_capable, struct bpf_token *token, int cap) @ bpf_lsm.c:17
16: (bf) r0 = r6                      ; R0_w=scalar(id=1,smin=smin32=-128,smax=smax32=127) R6_w=scalar(id=1,smin=smin32=-128,smax=smax32=127)
17: (95) exit
At program exit the register R0 has smin=-128 smax=127 should have been in [-4095, 0]

To avoid this failure, change the variable type from bool to int.

Signed-off-by: Xu Kuohai <[e-mail]>
---
 tools/testing/selftests/bpf/progs/token_lsm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

diff --git a/tools/testing/selftests/bpf/progs/token_lsm.c b/tools/testing/selftests/bpf/progs/token_lsm.c
index e4d59b6ba743..a6002d073b1b 100644
--- a/tools/testing/selftests/bpf/progs/token_lsm.c
+++ b/tools/testing/selftests/bpf/progs/token_lsm.c
@@ -8,8 +8,8 @@ 
 char _license[] SEC("license") = "GPL";
 
 int my_pid;
-bool reject_capable;
-bool reject_cmd;
+int reject_capable;
+int reject_cmd;
 
 SEC("lsm/bpf_token_capable")
 int BPF_PROG(token_capable, struct bpf_token *token, int cap)