selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 94 insertions, 0 deletions

diff --git a/arch/x86/lib/msr-reg.S b/arch/x86/lib/msr-reg.S
new file mode 100644
index 000000000..5ef849489
--- /dev/null
+++ b/arch/x86/lib/msr-reg.S
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+#include <linux/errno.h>
+#include <linux/cfi_types.h>
+#include <asm/asm.h>
+#include <asm/msr.h>
+
+#ifdef CONFIG_X86_64
+/*
+ * int {rdmsr,wrmsr}_safe_regs(u32 gprs[8]);
+ *
+ * reg layout: u32 gprs[eax, ecx, edx, ebx, esp, ebp, esi, edi]
+ *
+ */
+.macro op_safe_regs op
+SYM_TYPED_FUNC_START(\op\()_safe_regs)
+	pushq %rbx
+	pushq %r12
+	movq	%rdi, %r10	/* Save pointer */
+	xorl	%r11d, %r11d	/* Return value */
+	movl    (%rdi), %eax
+	movl    4(%rdi), %ecx
+	movl    8(%rdi), %edx
+	movl    12(%rdi), %ebx
+	movl    20(%rdi), %r12d
+	movl    24(%rdi), %esi
+	movl    28(%rdi), %edi
+1:	\op
+2:	movl    %eax, (%r10)
+	movl	%r11d, %eax	/* Return value */
+	movl    %ecx, 4(%r10)
+	movl    %edx, 8(%r10)
+	movl    %ebx, 12(%r10)
+	movl    %r12d, 20(%r10)
+	movl    %esi, 24(%r10)
+	movl    %edi, 28(%r10)
+	popq %r12
+	popq %rbx
+	RET
+3:
+	movl    $-EIO, %r11d
+	jmp     2b
+
+	_ASM_EXTABLE(1b, 3b)
+SYM_FUNC_END(\op\()_safe_regs)
+.endm
+
+#else /* X86_32 */
+
+.macro op_safe_regs op
+SYM_FUNC_START(\op\()_safe_regs)
+	pushl %ebx
+	pushl %ebp
+	pushl %esi
+	pushl %edi
+	pushl $0              /* Return value */
+	pushl %eax
+	movl    4(%eax), %ecx
+	movl    8(%eax), %edx
+	movl    12(%eax), %ebx
+	movl    20(%eax), %ebp
+	movl    24(%eax), %esi
+	movl    28(%eax), %edi
+	movl    (%eax), %eax
+1:	\op
+2:	pushl %eax
+	movl    4(%esp), %eax
+	popl (%eax)
+	addl    $4, %esp
+	movl    %ecx, 4(%eax)
+	movl    %edx, 8(%eax)
+	movl    %ebx, 12(%eax)
+	movl    %ebp, 20(%eax)
+	movl    %esi, 24(%eax)
+	movl    %edi, 28(%eax)
+	popl %eax
+	popl %edi
+	popl %esi
+	popl %ebp
+	popl %ebx
+	RET
+3:
+	movl    $-EIO, 4(%esp)
+	jmp     2b
+
+	_ASM_EXTABLE(1b, 3b)
+SYM_FUNC_END(\op\()_safe_regs)
+.endm
+
+#endif
+
+op_safe_regs rdmsr
+op_safe_regs wrmsr
+