linux-kernel - [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write

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

Date:   Mon,  3 Feb 2020 23:16:05 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Laight <David.Laight@...lab.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write

If split lock detect is enabled (warn/fatal), #AC handler calls die()
when split lock happens in kernel.

A sane guest should never tigger emulation on a split-lock access, but
it cannot prevent malicous guest from doing this. So just emulating the
access as a write if it's a split-lock access to avoid malicous guest
polluting the kernel log.

More detail analysis can be found:
https://lkml.kernel.org/r/20200131200134.GD18946@linux.intel.com

Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
---
 arch/x86/kvm/x86.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2d3be7f3ad67..821b7404c0fd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5847,6 +5847,13 @@ static int emulator_write_emulated(struct x86_emulate_ctxt *ctxt,
 	(cmpxchg64((u64 *)(ptr), *(u64 *)(old), *(u64 *)(new)) == *(u64 *)(old))
 #endif
 
+static inline bool across_cache_line_access(gpa_t gpa, unsigned int bytes)
+{
+	unsigned int cache_line_size = cache_line_size();
+
+	return (gpa & (cache_line_size - 1)) + bytes > cache_line_size;
+}
+
 static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 				     unsigned long addr,
 				     const void *old,
@@ -5873,6 +5880,10 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 	if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
 		goto emul_write;
 
+	if (get_split_lock_detect_state() != sld_off &&
+	    across_cache_line_access(gpa, bytes))
+		goto emul_write;
+
 	if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))
 		goto emul_write;
 
-- 
2.23.0