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Sat, 11 Oct 2025 00:22:16 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFolHZDr/hilaBuYpn/xuoq2o2sw7kV6NjzNz8W0VyvOLJC7Gg7q9fNdh7/o1Vu9xzKl0xFkQ== X-Received: by 2002:a17:907:c05:b0:b3e:fe8f:764 with SMTP id a640c23a62f3a-b50ac0cc05fmr1478846566b.32.1760167334852; Sat, 11 Oct 2025 00:22:14 -0700 (PDT) Received: from [192.168.10.48] ([151.49.231.162]) by smtp.googlemail.com with ESMTPSA id a640c23a62f3a-b55d5cac043sm418010166b.13.2025.10.11.00.22.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 11 Oct 2025 00:22:14 -0700 (PDT) Message-ID: Date: Sat, 11 Oct 2025 09:22:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] i386/tcg/smm_helper: Properly apply DR values on SMM entry / exit To: YiFei Zhu , qemu-devel@nongnu.org Cc: Zhao Liu , Richard Henderson , Eduardo Habkost , qemu-stable@nongnu.org, unvariant.winter@gmail.com, YiFei Zhu References: <2bacb9b24e9d337dbe48791aa25d349eb9c52c3a.1758794468.git.zhuyifei@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.441, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 9/25/25 12:30, YiFei Zhu wrote: > do_smm_enter and helper_rsm sets the env->dr, but does not sync the > values with cpu_x86_update_dr7. A malicious kernel may control the > instruction pointer in SMM by setting a breakpoint on the SMI > entry point, and after do_smm_enter cpu->breakpoints contains the > stale breakpoint; and because IDT is not reloaded upon SMI entry, > the debug exception handler controlled by the malicious kernel > is invoked. > > Fixes: 01df040b5247 ("x86: Debug register emulation (Jan Kiszka)") > Reported-by: unvariant.winter@gmail.com > Signed-off-by: YiFei Zhu Applied, thanks! Paolo > --- > target/i386/tcg/system/smm_helper.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/target/i386/tcg/system/smm_helper.c b/target/i386/tcg/system/smm_helper.c > index 251eb7856c..fb028a8272 100644 > --- a/target/i386/tcg/system/smm_helper.c > +++ b/target/i386/tcg/system/smm_helper.c > @@ -168,7 +168,7 @@ void do_smm_enter(X86CPU *cpu) > env->cr[0] & ~(CR0_PE_MASK | CR0_EM_MASK | CR0_TS_MASK | > CR0_PG_MASK)); > cpu_x86_update_cr4(env, 0); > - env->dr[7] = 0x00000400; > + helper_set_dr(env, 7, 0x00000400); > > cpu_x86_load_seg_cache(env, R_CS, (env->smbase >> 4) & 0xffff, env->smbase, > 0xffffffff, > @@ -233,8 +233,8 @@ void helper_rsm(CPUX86State *env) > env->eip = x86_ldq_phys(cs, sm_state + 0x7f78); > cpu_load_eflags(env, x86_ldl_phys(cs, sm_state + 0x7f70), > ~(CC_O | CC_S | CC_Z | CC_A | CC_P | CC_C | DF_MASK)); > - env->dr[6] = x86_ldl_phys(cs, sm_state + 0x7f68); > - env->dr[7] = x86_ldl_phys(cs, sm_state + 0x7f60); > + helper_set_dr(env, 6, x86_ldl_phys(cs, sm_state + 0x7f68)); > + helper_set_dr(env, 7, x86_ldl_phys(cs, sm_state + 0x7f60)); > > cpu_x86_update_cr4(env, x86_ldl_phys(cs, sm_state + 0x7f48)); > cpu_x86_update_cr3(env, x86_ldq_phys(cs, sm_state + 0x7f50)); > @@ -268,8 +268,8 @@ void helper_rsm(CPUX86State *env) > env->regs[R_EDX] = x86_ldl_phys(cs, sm_state + 0x7fd8); > env->regs[R_ECX] = x86_ldl_phys(cs, sm_state + 0x7fd4); > env->regs[R_EAX] = x86_ldl_phys(cs, sm_state + 0x7fd0); > - env->dr[6] = x86_ldl_phys(cs, sm_state + 0x7fcc); > - env->dr[7] = x86_ldl_phys(cs, sm_state + 0x7fc8); > + helper_set_dr(env, 6, x86_ldl_phys(cs, sm_state + 0x7fcc)); > + helper_set_dr(env, 7, x86_ldl_phys(cs, sm_state + 0x7fc8)); > > env->tr.selector = x86_ldl_phys(cs, sm_state + 0x7fc4) & 0xffff; > env->tr.base = x86_ldl_phys(cs, sm_state + 0x7f64);