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selftests/bpf: add tests for PTR_TO_FLOW_KEYS offset bounds

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Add verifier tests covering pointer arithmetic on a PTR_TO_FLOW_KEYS
register. This covers the bpf-next regression where an out-of-bounds
constant offset introduced as flow_keys += K and then dereferenced at
insn->off 0 was accepted, while the equivalent flow_keys + K direct offset
was rejected.

The tests check that in-bounds constant arithmetic on the keys pointer is
still accepted, out-of-bounds constant arithmetic is rejected for both read
and write, and a truly varying offset from bpf_get_prandom_u32() remains
rejected by the existing PTR_TO_FLOW_KEYS pointer arithmetic rules.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260606-c3-01-v3-v3-2-97c51f592f15@mails.tsinghua.edu.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Nuoqi Gui 2026-06-06 18:50:38 +08:00 committed by Alexei Starovoitov
parent 37363191cb
commit 3ce6b42458
2 changed files with 99 additions and 0 deletions
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2
tools/testing/selftests/bpf/prog_tests/verifier.c
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@ -38,6 +38,7 @@
#include "verifier_div0.skel.h"
#include "verifier_div_mod_bounds.skel.h"
#include "verifier_div_overflow.skel.h"
#include "verifier_flow_keys.skel.h"
#include "verifier_global_subprogs.skel.h"
#include "verifier_global_ptr_args.skel.h"
#include "verifier_gotol.skel.h"
@ -190,6 +191,7 @@ void test_verifier_direct_stack_access_wraparound(void) { RUN(verifier_direct_st
void test_verifier_div0(void) { RUN(verifier_div0); }
void test_verifier_div_mod_bounds(void) { RUN(verifier_div_mod_bounds); }
void test_verifier_div_overflow(void) { RUN(verifier_div_overflow); }
void test_verifier_flow_keys(void) { RUN(verifier_flow_keys); }
void test_verifier_global_subprogs(void) { RUN(verifier_global_subprogs); }
void test_verifier_global_ptr_args(void) { RUN(verifier_global_ptr_args); }
void test_verifier_gotol(void) { RUN(verifier_gotol); }

97
tools/testing/selftests/bpf/progs/verifier_flow_keys.c Normal file
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@ -0,0 +1,97 @@
// SPDX-License-Identifier: GPL-2.0
/* Bounds checks for PTR_TO_FLOW_KEYS pointer arithmetic. */
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
/* sizeof(struct bpf_flow_keys) is well under 4096, so +0x1000 is OOB. */
SEC("flow_dissector")
__description("flow_keys: in-bounds constant pointer arithmetic accepted")
__success
__naked void flow_keys_const_inbounds(void)
{
asm volatile (" \
r1 = *(u64 *)(r1 + %[flow_keys]); \
r1 += 8; \
r0 = *(u64 *)(r1 + 0); \
r0 = 0; \
exit; \
" :
: __imm_const(flow_keys, offsetof(struct __sk_buff, flow_keys))
: __clobber_all);
}
SEC("flow_dissector")
__description("flow_keys: OOB via constant pointer arithmetic rejected")
__failure __msg("invalid access to flow keys off=4096 size=8")
__naked void flow_keys_const_oob_read(void)
{
asm volatile (" \
r1 = *(u64 *)(r1 + %[flow_keys]); \
r1 += 4096; \
r0 = *(u64 *)(r1 + 0); \
r0 = 0; \
exit; \
" :
: __imm_const(flow_keys, offsetof(struct __sk_buff, flow_keys))
: __clobber_all);
}
SEC("flow_dissector")
__description("flow_keys: OOB write via constant pointer arithmetic rejected")
__failure __msg("invalid access to flow keys off=4096 size=8")
__naked void flow_keys_const_oob_write(void)
{
asm volatile (" \
r1 = *(u64 *)(r1 + %[flow_keys]); \
r1 += 4096; \
r2 = 0; \
*(u64 *)(r1 + 0) = r2; \
r0 = 0; \
exit; \
" :
: __imm_const(flow_keys, offsetof(struct __sk_buff, flow_keys))
: __clobber_all);
}
/* Equivalent OOB expressed directly in insn->off; this form was always
* rejected and is kept to show both forms now share one diagnostic.
*/
SEC("flow_dissector")
__description("flow_keys: OOB via insn->off rejected")
__failure __msg("invalid access to flow keys off=4096 size=8")
__naked void flow_keys_insn_off_oob(void)
{
asm volatile (" \
r1 = *(u64 *)(r1 + %[flow_keys]); \
r0 = *(u64 *)(r1 + 4096); \
r0 = 0; \
exit; \
" :
: __imm_const(flow_keys, offsetof(struct __sk_buff, flow_keys))
: __clobber_all);
}
SEC("flow_dissector")
__description("flow_keys: variable pointer arithmetic rejected")
__failure __msg("R1 pointer arithmetic on flow_keys prohibited")
__naked void flow_keys_var_read(void)
{
asm volatile (" \
r6 = r1; \
call %[bpf_get_prandom_u32]; \
r0 &= 0xFFFF; \
r1 = *(u64 *)(r6 + %[flow_keys]); \
r1 += r0; \
r0 = *(u64 *)(r1 + 0); \
r0 = 0; \
exit; \
" :
: __imm_const(flow_keys, offsetof(struct __sk_buff, flow_keys)),
__imm(bpf_get_prandom_u32)
: __clobber_all);
}
char _license[] SEC("license") = "GPL";