[PATCH bpf-next] selftests/bpf: ignore call depth accounting for retbleed in verifier tests

["Alexis Lothoré (eBPF Foundation)" <alexis.lothore@bootlin.com>]

When running the selftests on a retbleed-affected platform (eg:
Skylake), with call depth accounting enabled
(CONFIG_CALL_DEPTH_TRACKING=y) _and_ with retbleed=stuff, some verifier
selftests fail to validate the jited instructions. For example:

  MATCHED    SUBSTR: '	endbr64'
  MATCHED    SUBSTR: '	nopl	(%rax,%rax)'
  MATCHED    SUBSTR: '	xorq	%rax, %rax'
  MATCHED    SUBSTR: '	pushq	%rbp'
  MATCHED    SUBSTR: '	movq	%rsp, %rbp'
  MATCHED    SUBSTR: '	endbr64'
  MATCHED    SUBSTR: '	cmpq	$0x21, %rax'
  MATCHED    SUBSTR: '	ja	L0'
  MATCHED    SUBSTR: '	pushq	%rax'
  MATCHED    SUBSTR: '	movq	%rsp, %rax'
  MATCHED    SUBSTR: '	jmp	L1'
  MATCHED    SUBSTR: 'L0:	pushq	%rax'
  MATCHED    SUBSTR: 'L1:	pushq	%rax'
  MATCHED    SUBSTR: '	movq	-0x10(%rbp), %rax'
  WRONG LINE  REGEX: '	callq	0x{{.*}}'

Those affected selftests allways fail on some call instruction: this
failure is due to the JIT compiler emitting call depth accounting for
retbleed mitigation (see x86_call_depth_emit_accounting calls in
bpf_jit_comp.c), resulting in an additional instruction being inserted
in front of every call instruction, similar to this one:

  sarq    $0x5, %gs:-0x39882741(%rip)

Fix those selftests by allowing them to ignore this possibly present
call depth accounting instruction.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
---
 tools/testing/selftests/bpf/progs/verifier_private_stack.c | 5 +++++
 tools/testing/selftests/bpf/progs/verifier_tailcall_jit.c  | 1 +
 2 files changed, 6 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_private_stack.c b/tools/testing/selftests/bpf/progs/verifier_private_stack.c
index 046f7445a458..bb8206e10880 100644
--- a/tools/testing/selftests/bpf/progs/verifier_private_stack.c
+++ b/tools/testing/selftests/bpf/progs/verifier_private_stack.c
@@ -94,6 +94,7 @@ __jited("	addq	%gs:{{.*}}, %r9")
 __jited("	movl	$0x2a, %edi")
 __jited("	movq	%rdi, -0x200(%r9)")
 __jited("	pushq	%r9")
+__jited("...")
 __jited("	callq	0x{{.*}}")
 __jited("	popq	%r9")
 __jited("	xorl	%eax, %eax")
@@ -153,11 +154,13 @@ __jited("	endbr64")
 __jited("	movabsq	$0x{{.*}}, %r9")
 __jited("	addq	%gs:{{.*}}, %r9")
 __jited("	pushq	%r9")
+__jited("...")
 __jited("	callq")
 __jited("	popq	%r9")
 __jited("	movl	$0x2a, %edi")
 __jited("	movq	%rdi, -0x200(%r9)")
 __jited("	pushq	%r9")
+__jited("...")
 __jited("	callq")
 __jited("	popq	%r9")
 __arch_arm64
@@ -199,6 +202,7 @@ __description("Private stack, exception in main prog")
 __success __retval(0)
 __arch_x86_64
 __jited("	pushq	%r9")
+__jited("...")
 __jited("	callq")
 __jited("	popq	%r9")
 __arch_arm64
@@ -246,6 +250,7 @@ __success __retval(0)
 __arch_x86_64
 __jited("	movq	%rdi, -0x200(%r9)")
 __jited("	pushq	%r9")
+__jited("...")
 __jited("	callq")
 __jited("	popq	%r9")
 __arch_arm64
diff --git a/tools/testing/selftests/bpf/progs/verifier_tailcall_jit.c b/tools/testing/selftests/bpf/progs/verifier_tailcall_jit.c
index 8d60c634a114..48fa34d2959f 100644
--- a/tools/testing/selftests/bpf/progs/verifier_tailcall_jit.c
+++ b/tools/testing/selftests/bpf/progs/verifier_tailcall_jit.c
@@ -56,6 +56,7 @@ __jited("L1:	pushq	%rax")			/* rbp[-16] = rax         */
  * (cause original rax might be clobbered by this point)
  */
 __jited("	movq	-0x10(%rbp), %rax")
+__jited("...")
 __jited("	callq	0x{{.*}}")		/* call to sub()          */
 __jited("	xorl	%eax, %eax")
 __jited("	leave")

---
base-commit: 4a8eaccfdd6f4ae4b0e8735664e9d3e5ce826329
change-id: 20260528-fix_tests_for_retbleed_stuff-c3c89b738e70

Best regards,
--  
Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>