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selftests/bpf: Tests for per-insn sync_linked_regs() precision tracking

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Add a few test cases to verify precision tracking for scalars gaining
range because of sync_linked_regs():
- check what happens when more than 6 registers might gain range in
  sync_linked_regs();
- check if precision is propagated correctly when operand of
  conditional jump gained range in sync_linked_regs() and one of
  linked registers is marked precise;
- check if precision is propagated correctly when operand of
  conditional jump gained range in sync_linked_regs() and a
  other-linked operand of the conditional jump is marked precise;
- add a minimized reproducer for precision tracking bug reported in [0];
- Check that mark_chain_precision() for one of the conditional jump
  operands does not trigger equal scalars precision propagation.

[0] https://lore.kernel.org/bpf/CAEf4BzZ0xidVCqB47XnkXcNhkPWF6_nTV7yt+_Lf0kcFEut2Mg@mail.gmail.com/

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240718202357.1746514-4-eddyz87@gmail.com
This commit is contained in:
Eduard Zingerman 2024-07-18 13:23:55 -07:00 committed by Andrii Nakryiko
parent 842edb5507
commit bebc17b1c0
1 changed files with 165 additions and 0 deletions
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165
tools/testing/selftests/bpf/progs/verifier_scalar_ids.c
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@ -47,6 +47,72 @@ __naked void linked_regs_bpf_k(void)
: __clobber_all);
}
/* Registers r{0,1,2} share same ID when 'if r1 > ...' insn is processed,
* check that verifier marks r{1,2} as precise while backtracking
* 'if r1 > ...' with r0 already marked.
*/
SEC("socket")
__success __log_level(2)
__flag(BPF_F_TEST_STATE_FREQ)
__msg("frame0: regs=r0 stack= before 5: (2d) if r1 > r3 goto pc+0")
__msg("frame0: parent state regs=r0,r1,r2,r3 stack=:")
__msg("frame0: regs=r0,r1,r2,r3 stack= before 4: (b7) r3 = 7")
__naked void linked_regs_bpf_x_src(void)
{
asm volatile (
/* r0 = random number up to 0xff */
"call %[bpf_ktime_get_ns];"
"r0 &= 0xff;"
/* tie r0.id == r1.id == r2.id */
"r1 = r0;"
"r2 = r0;"
"r3 = 7;"
"if r1 > r3 goto +0;"
/* force r0 to be precise, this eventually marks r1 and r2 as
* precise as well because of shared IDs
*/
"r4 = r10;"
"r4 += r0;"
"r0 = 0;"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* Registers r{0,1,2} share same ID when 'if r1 > r3' insn is processed,
* check that verifier marks r{0,1,2} as precise while backtracking
* 'if r1 > r3' with r3 already marked.
*/
SEC("socket")
__success __log_level(2)
__flag(BPF_F_TEST_STATE_FREQ)
__msg("frame0: regs=r3 stack= before 5: (2d) if r1 > r3 goto pc+0")
__msg("frame0: parent state regs=r0,r1,r2,r3 stack=:")
__msg("frame0: regs=r0,r1,r2,r3 stack= before 4: (b7) r3 = 7")
__naked void linked_regs_bpf_x_dst(void)
{
asm volatile (
/* r0 = random number up to 0xff */
"call %[bpf_ktime_get_ns];"
"r0 &= 0xff;"
/* tie r0.id == r1.id == r2.id */
"r1 = r0;"
"r2 = r0;"
"r3 = 7;"
"if r1 > r3 goto +0;"
/* force r0 to be precise, this eventually marks r1 and r2 as
* precise as well because of shared IDs
*/
"r4 = r10;"
"r4 += r3;"
"r0 = 0;"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* Same as linked_regs_bpf_k, but break one of the
* links, note that r1 is absent from regs=... in __msg below.
*/
@ -280,6 +346,105 @@ __naked void precision_two_ids(void)
: __clobber_all);
}
SEC("socket")
__success __log_level(2)
__flag(BPF_F_TEST_STATE_FREQ)
/* check thar r0 and r6 have different IDs after 'if',
* collect_linked_regs() can't tie more than 6 registers for a single insn.
*/
__msg("8: (25) if r0 > 0x7 goto pc+0 ; R0=scalar(id=1")
__msg("9: (bf) r6 = r6 ; R6_w=scalar(id=2")
/* check that r{0-5} are marked precise after 'if' */
__msg("frame0: regs=r0 stack= before 8: (25) if r0 > 0x7 goto pc+0")
__msg("frame0: parent state regs=r0,r1,r2,r3,r4,r5 stack=:")
__naked void linked_regs_too_many_regs(void)
{
asm volatile (
/* r0 = random number up to 0xff */
"call %[bpf_ktime_get_ns];"
"r0 &= 0xff;"
/* tie r{0-6} IDs */
"r1 = r0;"
"r2 = r0;"
"r3 = r0;"
"r4 = r0;"
"r5 = r0;"
"r6 = r0;"
/* propagate range for r{0-6} */
"if r0 > 7 goto +0;"
/* make r6 appear in the log */
"r6 = r6;"
/* force r0 to be precise,
* this would cause r{0-4} to be precise because of shared IDs
*/
"r7 = r10;"
"r7 += r0;"
"r0 = 0;"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
SEC("socket")
__failure __log_level(2)
__flag(BPF_F_TEST_STATE_FREQ)
__msg("regs=r7 stack= before 5: (3d) if r8 >= r0")
__msg("parent state regs=r0,r7,r8")
__msg("regs=r0,r7,r8 stack= before 4: (25) if r0 > 0x1")
__msg("div by zero")
__naked void linked_regs_broken_link_2(void)
{
asm volatile (
"call %[bpf_get_prandom_u32];"
"r7 = r0;"
"r8 = r0;"
"call %[bpf_get_prandom_u32];"
"if r0 > 1 goto +0;"
/* r7.id == r8.id,
* thus r7 precision implies r8 precision,
* which implies r0 precision because of the conditional below.
*/
"if r8 >= r0 goto 1f;"
/* break id relation between r7 and r8 */
"r8 += r8;"
/* make r7 precise */
"if r7 == 0 goto 1f;"
"r0 /= 0;"
"1:"
"r0 = 42;"
"exit;"
:
: __imm(bpf_get_prandom_u32)
: __clobber_all);
}
/* Check that mark_chain_precision() for one of the conditional jump
* operands does not trigger equal scalars precision propagation.
*/
SEC("socket")
__success __log_level(2)
__msg("3: (25) if r1 > 0x100 goto pc+0")
__msg("frame0: regs=r1 stack= before 2: (bf) r1 = r0")
__naked void cjmp_no_linked_regs_trigger(void)
{
asm volatile (
/* r0 = random number up to 0xff */
"call %[bpf_ktime_get_ns];"
"r0 &= 0xff;"
/* tie r0.id == r1.id */
"r1 = r0;"
/* the jump below would be predicted, thus r1 would be marked precise,
* this should not imply precision mark for r0
*/
"if r1 > 256 goto +0;"
"r0 = 0;"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* Verify that check_ids() is used by regsafe() for scalars.
*
* r9 = ... some pointer with range X ...