linux-kernel - [PATCH 7/7] KVM: selftests: Verify 'BS' bit checking in pending debug exception during VM entry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <3c0686934fc33ebb484aa5cc71443a22504df7ca.1757416809.git.houwenlong.hwl@antgroup.com>
Date: Wed, 10 Sep 2025 10:49:19 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: kvm@...r.kernel.org
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Shuah Khan <shuah@...nel.org>,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 7/7] KVM: selftests: Verify 'BS' bit checking in pending debug exception during VM entry

In the x86's debug_regs test, add a test case to cover the scenario where
single-step with STI in VMX sets the 'BS' bit in pending debug
exceptions for #DB interception and instruction emulation in both cases.

Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
---
 .../selftests/kvm/include/x86/processor.h     |  3 +-
 tools/testing/selftests/kvm/x86/debug_regs.c  | 41 +++++++++++++++++--
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 488d516c4f6f..f5827cca813e 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -34,7 +34,8 @@ extern uint64_t guest_tsc_khz;
 
 #define NMI_VECTOR		0x02
 
-#define X86_EFLAGS_FIXED	 (1u << 1)
+#define X86_EFLAGS_FIXED	(1u << 1)
+#define X86_EFLAGS_TF		(1u << 8)
 
 #define X86_CR4_VME		(1ul << 0)
 #define X86_CR4_PVI		(1ul << 1)
diff --git a/tools/testing/selftests/kvm/x86/debug_regs.c b/tools/testing/selftests/kvm/x86/debug_regs.c
index ba80b77c2869..60dea0116b21 100644
--- a/tools/testing/selftests/kvm/x86/debug_regs.c
+++ b/tools/testing/selftests/kvm/x86/debug_regs.c
@@ -15,11 +15,31 @@
 
 #define IRQ_VECTOR 0xAA
 
+#define  CAST_TO_RIP(v)  ((unsigned long long)&(v))
+
 /* For testing data access debug BP */
 uint32_t guest_value;
 
 extern unsigned char sw_bp, hw_bp, write_data, ss_start, bd_start;
-extern unsigned char fep_bd_start;
+extern unsigned char fep_bd_start, fep_sti_start, fep_sti_end;
+
+static void guest_db_handler(struct ex_regs *regs)
+{
+	static int count;
+	unsigned long target_rips[2] = {
+		CAST_TO_RIP(fep_sti_start),
+		CAST_TO_RIP(fep_sti_end),
+	};
+
+	__GUEST_ASSERT(regs->rip == target_rips[count], "STI: unexpected rip 0x%lx (should be 0x%lx)",
+		       regs->rip, target_rips[count]);
+	regs->rflags &= ~X86_EFLAGS_TF;
+	count++;
+}
+
+static void guest_irq_handler(struct ex_regs *regs)
+{
+}
 
 static void guest_code(void)
 {
@@ -69,13 +89,25 @@ static void guest_code(void)
 	if (is_forced_emulation_enabled) {
 		/* DR6.BD test for emulation */
 		asm volatile(KVM_FEP "fep_bd_start: mov %%dr0, %%rax" : : : "rax");
+
+		/* pending debug exceptions for emulation */
+		asm volatile("pushf\n\t"
+			     "orq $" __stringify(X86_EFLAGS_TF) ", (%rsp)\n\t"
+			     "popf\n\t"
+			     "sti\n\t"
+			     "fep_sti_start:"
+			     "cli\n\t"
+			     "pushf\n\t"
+			     "orq $" __stringify(X86_EFLAGS_TF) ", (%rsp)\n\t"
+			     "popf\n\t"
+			     KVM_FEP "sti\n\t"
+			     "fep_sti_end:"
+			     "cli\n\t");
 	}
 
 	GUEST_DONE();
 }
 
-#define  CAST_TO_RIP(v)  ((unsigned long long)&(v))
-
 static void vcpu_skip_insn(struct kvm_vcpu *vcpu, int insn_len)
 {
 	struct kvm_regs regs;
@@ -110,6 +142,9 @@ int main(void)
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 	run = vcpu->run;
 
+	vm_install_exception_handler(vm, DB_VECTOR, guest_db_handler);
+	vm_install_exception_handler(vm, IRQ_VECTOR, guest_irq_handler);
+
 	/* Test software BPs - int3 */
 	memset(&debug, 0, sizeof(debug));
 	debug.control = KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP;
-- 
2.31.1