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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id z11sm345567pfr.71.2020.07.14.18.40.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2020 18:40:31 -0700 (PDT) Date: Tue, 14 Jul 2020 18:40:30 -0700 From: Kees Cook To: Joerg Roedel Cc: x86@kernel.org, Joerg Roedel , hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Sean Christopherson , Martin Radev , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v4 70/75] x86/head/64: Don't call verify_cpu() on starting APs Message-ID: <202007141837.2B93BBD78@keescook> References: <20200714120917.11253-1-joro@8bytes.org> <20200714120917.11253-71-joro@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714120917.11253-71-joro@8bytes.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 14, 2020 at 02:09:12PM +0200, Joerg Roedel wrote: > From: Joerg Roedel > > The APs are not ready to handle exceptions when verify_cpu() is called > in secondary_startup_64. Eek, no. MSR_IA32_MISC_ENABLE_XD_DISABLE needs to be cleared very early during CPU startup; this can't just be skipped. Also, is UNWIND_HINT_EMPTY needed for the new target? -Kees > > Signed-off-by: Joerg Roedel > --- > arch/x86/include/asm/realmode.h | 1 + > arch/x86/kernel/head_64.S | 1 + > arch/x86/realmode/init.c | 6 ++++++ > 3 files changed, 8 insertions(+) > > diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h > index 6590394af309..5c97807c38a4 100644 > --- a/arch/x86/include/asm/realmode.h > +++ b/arch/x86/include/asm/realmode.h > @@ -69,6 +69,7 @@ extern unsigned char startup_32_smp[]; > extern unsigned char boot_gdt[]; > #else > extern unsigned char secondary_startup_64[]; > +extern unsigned char secondary_startup_64_no_verify[]; > #endif > > static inline size_t real_mode_size_needed(void) > diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S > index 5b577d6bce7a..8b43ed0592e8 100644 > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -165,6 +165,7 @@ SYM_CODE_START(secondary_startup_64) > /* Sanitize CPU configuration */ > call verify_cpu > > +SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) > /* > * Retrieve the modifier (SME encryption mask if SME is active) to be > * added to the initial pgdir entry that will be programmed into CR3. > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c > index 61a52b925d15..df701f87ddef 100644 > --- a/arch/x86/realmode/init.c > +++ b/arch/x86/realmode/init.c > @@ -46,6 +46,12 @@ static void sme_sev_setup_real_mode(struct trampoline_header *th) > th->flags |= TH_FLAGS_SME_ACTIVE; > > if (sev_es_active()) { > + /* > + * Skip the call to verify_cpu() in secondary_startup_64 as it > + * will cause #VC exceptions when the AP can't handle them yet. > + */ > + th->start = (u64) secondary_startup_64_no_verify; > + > if (sev_es_setup_ap_jump_table(real_mode_header)) > panic("Failed to update SEV-ES AP Jump Table"); > } > -- > 2.27.0 > -- Kees Cook