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selftests/bpf: check if max number of bpf_loop iterations is tracked 

commit 57e2a52deeb12ab84c15c6d0fb93638b5b94001b upstream.

Check that even if bpf_loop() callback simulation does not converge to
a specific state, verification could proceed via "brute force"
simulation of maximal number of callback calls.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20231121020701.26440-12-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eduard Zingerman 2023-11-21 04:07:01 +02:00 committed by Greg Kroah-Hartman
parent bfc5c19b4b
commit c7890937cf
1 changed files with 75 additions and 0 deletions
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75
tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c
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@ -164,4 +164,79 @@ int unsafe_find_vma(void *unused)
return choice_arr[loop_ctx.i];
}
static int iter_limit_cb(__u32 idx, struct num_context *ctx)
{
ctx->i++;
return 0;
}
SEC("?raw_tp")
__success
int bpf_loop_iter_limit_ok(void *unused)
{
struct num_context ctx = { .i = 0 };
bpf_loop(1, iter_limit_cb, &ctx, 0);
return choice_arr[ctx.i];
}
SEC("?raw_tp")
__failure __msg("invalid access to map value, value_size=2 off=2 size=1")
int bpf_loop_iter_limit_overflow(void *unused)
{
struct num_context ctx = { .i = 0 };
bpf_loop(2, iter_limit_cb, &ctx, 0);
return choice_arr[ctx.i];
}
static int iter_limit_level2a_cb(__u32 idx, struct num_context *ctx)
{
ctx->i += 100;
return 0;
}
static int iter_limit_level2b_cb(__u32 idx, struct num_context *ctx)
{
ctx->i += 10;
return 0;
}
static int iter_limit_level1_cb(__u32 idx, struct num_context *ctx)
{
ctx->i += 1;
bpf_loop(1, iter_limit_level2a_cb, ctx, 0);
bpf_loop(1, iter_limit_level2b_cb, ctx, 0);
return 0;
}
/* Check that path visiting every callback function once had been
* reached by verifier. Variables 'ctx{1,2}i' below serve as flags,
* with each decimal digit corresponding to a callback visit marker.
*/
SEC("socket")
__success __retval(111111)
int bpf_loop_iter_limit_nested(void *unused)
{
struct num_context ctx1 = { .i = 0 };
struct num_context ctx2 = { .i = 0 };
__u64 a, b, c;
bpf_loop(1, iter_limit_level1_cb, &ctx1, 0);
bpf_loop(1, iter_limit_level1_cb, &ctx2, 0);
a = ctx1.i;
b = ctx2.i;
/* Force 'ctx1.i' and 'ctx2.i' precise. */
c = choice_arr[(a + b) % 2];
/* This makes 'c' zero, but neither clang nor verifier know it. */
c /= 10;
/* Make sure that verifier does not visit 'impossible' states:
* enumerate all possible callback visit masks.
*/
if (a != 0 && a != 1 && a != 11 && a != 101 && a != 111 &&
b != 0 && b != 1 && b != 11 && b != 101 && b != 111)
asm volatile ("r0 /= 0;" ::: "r0");
return 1000 * a + b + c;
}
char _license[] SEC("license") = "GPL";