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, 85 insertions, 0 deletions

diff --git a/arch/arm64/kvm/trng.c b/arch/arm64/kvm/trng.c
new file mode 100644
index 000000000..99bdd7103
--- /dev/null
+++ b/arch/arm64/kvm/trng.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 Arm Ltd.
+
+#include <linux/arm-smccc.h>
+#include <linux/kvm_host.h>
+
+#include <asm/kvm_emulate.h>
+
+#include <kvm/arm_hypercalls.h>
+
+#define ARM_SMCCC_TRNG_VERSION_1_0	0x10000UL
+
+/* Those values are deliberately separate from the generic SMCCC definitions. */
+#define TRNG_SUCCESS			0UL
+#define TRNG_NOT_SUPPORTED		((unsigned long)-1)
+#define TRNG_INVALID_PARAMETER		((unsigned long)-2)
+#define TRNG_NO_ENTROPY			((unsigned long)-3)
+
+#define TRNG_MAX_BITS64			192
+
+static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
+	0x0d21e000, 0x4384, 0x11eb, 0x80, 0x70, 0x52, 0x44, 0x55, 0x4e, 0x5a, 0x4c);
+
+static int kvm_trng_do_rnd(struct kvm_vcpu *vcpu, int size)
+{
+	DECLARE_BITMAP(bits, TRNG_MAX_BITS64);
+	u32 num_bits = smccc_get_arg1(vcpu);
+	int i;
+
+	if (num_bits > 3 * size) {
+		smccc_set_retval(vcpu, TRNG_INVALID_PARAMETER, 0, 0, 0);
+		return 1;
+	}
+
+	/* get as many bits as we need to fulfil the request */
+	for (i = 0; i < DIV_ROUND_UP(num_bits, BITS_PER_LONG); i++)
+		bits[i] = get_random_long();
+
+	bitmap_clear(bits, num_bits, TRNG_MAX_BITS64 - num_bits);
+
+	if (size == 32)
+		smccc_set_retval(vcpu, TRNG_SUCCESS, lower_32_bits(bits[1]),
+				 upper_32_bits(bits[0]), lower_32_bits(bits[0]));
+	else
+		smccc_set_retval(vcpu, TRNG_SUCCESS, bits[2], bits[1], bits[0]);
+
+	memzero_explicit(bits, sizeof(bits));
+	return 1;
+}
+
+int kvm_trng_call(struct kvm_vcpu *vcpu)
+{
+	const __le32 *u = (__le32 *)arm_smc_trng_uuid.b;
+	u32 func_id = smccc_get_function(vcpu);
+	unsigned long val = TRNG_NOT_SUPPORTED;
+	int size = 64;
+
+	switch (func_id) {
+	case ARM_SMCCC_TRNG_VERSION:
+		val = ARM_SMCCC_TRNG_VERSION_1_0;
+		break;
+	case ARM_SMCCC_TRNG_FEATURES:
+		switch (smccc_get_arg1(vcpu)) {
+		case ARM_SMCCC_TRNG_VERSION:
+		case ARM_SMCCC_TRNG_FEATURES:
+		case ARM_SMCCC_TRNG_GET_UUID:
+		case ARM_SMCCC_TRNG_RND32:
+		case ARM_SMCCC_TRNG_RND64:
+			val = TRNG_SUCCESS;
+		}
+		break;
+	case ARM_SMCCC_TRNG_GET_UUID:
+		smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
+				 le32_to_cpu(u[2]), le32_to_cpu(u[3]));
+		return 1;
+	case ARM_SMCCC_TRNG_RND32:
+		size = 32;
+		fallthrough;
+	case ARM_SMCCC_TRNG_RND64:
+		return kvm_trng_do_rnd(vcpu, size);
+	}
+
+	smccc_set_retval(vcpu, val, 0, 0, 0);
+	return 1;
+}