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From: Brijesh Singh <brijesh.singh@amd.com>
To: x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org, linux-crypto@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	tony.luck@intel.com, npmccallum@redhat.com,
	brijesh.ksingh@gmail.com, Brijesh Singh <brijesh.singh@amd.com>
Subject: [PATCH Part1 RFC v4 21/36] x86/head/64: set up a startup %gs for stack protector
Date: Wed,  7 Jul 2021 13:14:51 -0500	[thread overview]
Message-ID: <20210707181506.30489-22-brijesh.singh@amd.com> (raw)
In-Reply-To: <20210707181506.30489-1-brijesh.singh@amd.com>

From: Michael Roth <michael.roth@amd.com>

As of commit 103a4908ad4d ("x86/head/64: Disable stack protection for
head$(BITS).o") kernel/head64.c is compiled with -fno-stack-protector
to allow a call to set_bringup_idt_handler(), which would otherwise
have stack protection enabled with CONFIG_STACKPROTECTOR_STRONG. While
sufficient for that case, this will still cause issues if we attempt to
call out to any external functions that were compiled with stack
protection enabled that in-turn make stack-protected calls, or if the
exception handlers set up by set_bringup_idt_handler() make calls to
stack-protected functions.

Subsequent patches for SEV-SNP CPUID validation support will introduce
both such cases. Attempting to disable stack protection for everything
in scope to address that is prohibitive since much of the code, like
SEV-ES #VC handler, is shared code that remains in use after boot and
could benefit from having stack protection enabled. Attempting to inline
calls is brittle and can quickly balloon out to library/helper code
where that's not really an option.

Instead, set up %gs to point a buffer that stack protector can use for
canary values when needed.

In doing so, it's likely we can stop using -no-stack-protector for
head64.c, but that hasn't been tested yet, and head32.c would need a
similar solution to be safe, so that is left as a potential follow-up.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/kernel/head64.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index f4c3e632345a..8615418f98f1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -74,6 +74,9 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
 	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(0xc093, 0, 0xfffff),
 };
 
+/* For use by stack protector code before switching to virtual addresses */
+static char startup_gs_area[64];
+
 /*
  * Address needs to be set at runtime because it references the startup_gdt
  * while the kernel still uses a direct mapping.
@@ -598,6 +601,8 @@ void early_setup_idt(void)
  */
 void __head startup_64_setup_env(unsigned long physbase)
 {
+	u64 gs_area = (u64)fixup_pointer(startup_gs_area, physbase);
+
 	/* Load GDT */
 	startup_gdt_descr.address = (unsigned long)fixup_pointer(startup_gdt, physbase);
 	native_load_gdt(&startup_gdt_descr);
@@ -605,7 +610,18 @@ void __head startup_64_setup_env(unsigned long physbase)
 	/* New GDT is live - reload data segment registers */
 	asm volatile("movl %%eax, %%ds\n"
 		     "movl %%eax, %%ss\n"
-		     "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
+		     "movl %%eax, %%es\n"
+		     "movl %%eax, %%gs\n" : : "a"(__KERNEL_DS) : "memory");
+
+	/*
+	 * GCC stack protection needs a place to store canary values. The
+	 * default is %gs:0x28, which is what the kernel currently uses.
+	 * Point GS base to a buffer that can be used for this purpose.
+	 * Note that newer GCCs now allow this location to be configured,
+	 * so if we change from the default in the future we need to ensure
+	 * that this buffer overlaps whatever address ends up being used.
+	 */
+	native_wrmsr(MSR_GS_BASE, gs_area, gs_area >> 32);
 
 	startup_64_load_idt(physbase);
 }
-- 
2.17.1


  parent reply	other threads:[~2021-07-07 18:16 UTC|newest]

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-07 18:14 [PATCH Part1 RFC v4 00/36] Add AMD Secure Nested Paging (SEV-SNP) Guest Support Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 01/36] x86/sev: shorten GHCB terminate macro names Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 02/36] x86/sev: Save the negotiated GHCB version Brijesh Singh
2021-08-10  9:17   ` Borislav Petkov
2021-08-10 13:15     ` Brijesh Singh
2021-08-10 10:01   ` Borislav Petkov
2021-08-10 13:17     ` Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 03/36] x86/sev: Add support for hypervisor feature VMGEXIT Brijesh Singh
2021-08-10 11:22   ` Borislav Petkov
2021-08-10 13:39     ` Brijesh Singh
2021-08-10 14:03       ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 04/36] x86/mm: Add sev_feature_enabled() helper Brijesh Singh
2021-07-08  8:50   ` Dr. David Alan Gilbert
2021-07-08  8:53     ` Paolo Bonzini
2021-08-10 11:25   ` Borislav Petkov
2021-08-10 14:57     ` Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 05/36] x86/sev: Define the Linux specific guest termination reasons Brijesh Singh
2021-08-10 11:33   ` Borislav Petkov
2021-08-10 14:59     ` Brijesh Singh
2021-08-10 19:30       ` Tom Lendacky
2021-08-10 21:52         ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 06/36] x86/sev: check SEV-SNP features support Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 07/36] x86/sev: Add a helper for the PVALIDATE instruction Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 08/36] x86/sev: check the vmpl level Brijesh Singh
2021-08-13  7:25   ` Borislav Petkov
2021-08-13 13:13     ` Brijesh Singh
2021-08-13 15:16       ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 09/36] x86/compressed: Add helper for validating pages in the decompression stage Brijesh Singh
2021-08-13 10:22   ` Borislav Petkov
2021-08-13 14:21     ` Brijesh Singh
2021-08-13 15:19       ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 10/36] x86/compressed: Register GHCB memory when SEV-SNP is active Brijesh Singh
2021-08-13 10:47   ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 11/36] x86/sev: " Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 12/36] x86/sev: Add helper for validating pages in early enc attribute changes Brijesh Singh
2021-08-13 11:13   ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 13/36] x86/kernel: Make the bss.decrypted section shared in RMP table Brijesh Singh
2021-08-13 17:09   ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 14/36] x86/kernel: Validate rom memory before accessing when SEV-SNP is active Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 15/36] x86/mm: Add support to validate memory when changing C-bit Brijesh Singh
2021-08-17 17:27   ` Borislav Petkov
2021-08-17 18:07     ` Brijesh Singh
2021-08-17 18:17       ` Borislav Petkov
2021-08-17 18:18         ` Brijesh Singh
2021-08-17 20:34     ` Brijesh Singh
2021-08-17 20:44       ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 16/36] KVM: SVM: define new SEV_FEATURES field in the VMCB Save State Area Brijesh Singh
2021-08-17 17:54   ` Borislav Petkov
2021-08-17 17:59     ` Borislav Petkov
2021-08-17 18:11     ` Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 17/36] KVM: SVM: Create a separate mapping for the SEV-ES save area Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 18/36] KVM: SVM: Create a separate mapping for the GHCB " Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 19/36] KVM: SVM: Update the SEV-ES save area mapping Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 20/36] x86/sev: Use SEV-SNP AP creation to start secondary CPUs Brijesh Singh
2021-08-17 20:04   ` Borislav Petkov
2021-08-17 22:13     ` Tom Lendacky
2021-08-18  8:38       ` Borislav Petkov
2021-07-07 18:14 ` Brijesh Singh [this message]
2021-08-19  9:34   ` [PATCH Part1 RFC v4 21/36] x86/head/64: set up a startup %gs for stack protector Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 22/36] x86/sev: move MSR-based VMGEXITs for CPUID to helper Brijesh Singh
2021-08-19  9:45   ` Borislav Petkov
2021-08-19 15:37     ` Michael Roth
2021-08-19 16:46       ` Borislav Petkov
2021-08-20  3:29         ` Michael Roth
2021-08-23  4:50           ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 23/36] KVM: x86: move lookup of indexed CPUID leafs " Brijesh Singh
2021-08-19 10:07   ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 24/36] x86/compressed/acpi: move EFI config table access to common code Brijesh Singh
2021-08-19 10:47   ` Borislav Petkov
2021-08-19 14:58     ` Michael Roth
2021-08-19 17:09       ` Borislav Petkov
2021-08-19 23:42         ` Michael Roth
2021-08-23  4:52           ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 25/36] x86/boot: Add Confidential Computing type to setup_data Brijesh Singh
2021-08-19 11:06   ` Borislav Petkov
2021-07-07 18:14 ` [PATCH Part1 RFC v4 26/36] x86/compressed/64: enable SEV-SNP-validated CPUID in #VC handler Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 27/36] x86/boot: add a pointer to Confidential Computing blob in bootparams Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 28/36] x86/compressed/64: store Confidential Computing blob address " Brijesh Singh
2021-07-07 18:14 ` [PATCH Part1 RFC v4 29/36] x86/compressed/64: add identity mapping for Confidential Computing blob Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 30/36] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 31/36] x86/sev: Provide support for SNP guest request NAEs Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 32/36] x86/sev: Add snp_msg_seqno() helper Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 33/36] x86/sev: Register SNP guest request platform device Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 34/36] virt: Add SEV-SNP guest driver Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 35/36] virt: sevguest: Add support to derive key Brijesh Singh
2021-07-07 18:15 ` [PATCH Part1 RFC v4 36/36] virt: sevguest: Add support to get extended report Brijesh Singh

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