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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
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>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Andi Kleen <ak@linux.intel.com>,
	tony.luck@intel.com, marcorr@google.com,
	sathyanarayanan.kuppuswamy@linux.intel.com,
	Brijesh Singh <brijesh.singh@amd.com>
Subject: [PATCH Part1 v5 23/38] x86/head/64: set up a startup %gs for stack protector
Date: Fri, 20 Aug 2021 10:19:18 -0500	[thread overview]
Message-ID: <20210820151933.22401-24-brijesh.singh@amd.com> (raw)
In-Reply-To: <20210820151933.22401-1-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/Makefile |  2 +-
 arch/x86/kernel/head64.c | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 3e625c61f008..5abdfd0dbbc3 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -46,7 +46,7 @@ endif
 # non-deterministic coverage.
 KCOV_INSTRUMENT		:= n
 
-CFLAGS_head$(BITS).o	+= -fno-stack-protector
+CFLAGS_head32.o		+= -fno-stack-protector
 
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index a1711c4594fa..f1b76a54c84e 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -74,6 +74,11 @@ 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 */
+#if CONFIG_STACKPROTECTOR
+static char startup_gs_area[64];
+#endif
+
 /*
  * Address needs to be set at runtime because it references the startup_gdt
  * while the kernel still uses a direct mapping.
@@ -605,6 +610,8 @@ 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);
@@ -614,5 +621,18 @@ void __head startup_64_setup_env(unsigned long physbase)
 		     "movl %%eax, %%ss\n"
 		     "movl %%eax, %%es\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.
+	 */
+#if CONFIG_STACKPROTECTOR
+	asm volatile("movl %%eax, %%gs\n" : : "a"(__KERNEL_DS) : "memory");
+	native_wrmsr(MSR_GS_BASE, gs_area, gs_area >> 32);
+#endif
+
 	startup_64_load_idt(physbase);
 }
-- 
2.17.1


  parent reply	other threads:[~2021-08-20 15:22 UTC|newest]

Thread overview: 123+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20 15:18 [PATCH Part1 v5 00/38] Add AMD Secure Nested Paging (SEV-SNP) Guest Support Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 01/38] x86/mm: Add sev_feature_enabled() helper Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 02/38] x86/sev: Shorten GHCB terminate macro names Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 03/38] x86/sev: Get rid of excessive use of defines Brijesh Singh
2021-08-20 15:18 ` [PATCH Part1 v5 04/38] x86/head64: Carve out the guest encryption postprocessing into a helper Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 05/38] x86/sev: Define the Linux specific guest termination reasons Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 06/38] x86/sev: Save the negotiated GHCB version Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 07/38] x86/sev: Add support for hypervisor feature VMGEXIT Brijesh Singh
2021-08-23  9:47   ` Borislav Petkov
2021-08-23 18:25     ` Brijesh Singh
2021-08-23 18:34       ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 08/38] x86/sev: Check SEV-SNP features support Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 09/38] x86/sev: Add a helper for the PVALIDATE instruction Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 10/38] x86/sev: Check the vmpl level Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 11/38] x86/compressed: Add helper for validating pages in the decompression stage Brijesh Singh
2021-08-23 14:16   ` Borislav Petkov
2021-08-23 18:55     ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 12/38] x86/compressed: Register GHCB memory when SEV-SNP is active Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 13/38] x86/sev: " Brijesh Singh
2021-08-23 17:35   ` Borislav Petkov
2021-08-23 18:56     ` Brijesh Singh
2021-08-23 19:45       ` [PATCH] x86/sev: Remove do_early_exception() forward declarations Borislav Petkov
2021-08-23 20:06         ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 14/38] x86/sev: Add helper for validating pages in early enc attribute changes Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 15/38] x86/kernel: Make the bss.decrypted section shared in RMP table Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 16/38] x86/kernel: Validate rom memory before accessing when SEV-SNP is active Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory when changing C-bit Brijesh Singh
2021-08-25 11:06   ` Borislav Petkov
2021-08-25 13:54     ` Brijesh Singh
2021-08-25 14:00       ` Borislav Petkov
2021-08-27 17:09   ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 18/38] KVM: SVM: Define sev_features and vmpl field in the VMSA Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 19/38] KVM: SVM: Create a separate mapping for the SEV-ES save area Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 20/38] KVM: SVM: Create a separate mapping for the GHCB " Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 21/38] KVM: SVM: Update the SEV-ES save area mapping Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 22/38] x86/sev: Use SEV-SNP AP creation to start secondary CPUs Brijesh Singh
2021-08-20 15:19 ` Brijesh Singh [this message]
2021-08-25 14:29   ` [PATCH Part1 v5 23/38] x86/head/64: set up a startup %gs for stack protector Borislav Petkov
2021-08-25 15:18     ` Michael Roth
2021-08-25 16:29       ` Borislav Petkov
2021-08-27 13:38         ` Michael Roth
2021-08-31  8:03           ` Borislav Petkov
2021-08-31 23:30             ` Michael Roth
2021-08-25 15:07   ` Joerg Roedel
2021-08-25 17:07     ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 24/38] x86/sev: move MSR-based VMGEXITs for CPUID to helper Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 25/38] KVM: x86: move lookup of indexed CPUID leafs " Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 26/38] x86/compressed/acpi: move EFI config table access to common code Brijesh Singh
2021-08-25 15:18   ` Borislav Petkov
2021-08-25 17:14     ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 27/38] x86/boot: Add Confidential Computing type to setup_data Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 28/38] x86/compressed/64: enable SEV-SNP-validated CPUID in #VC handler Brijesh Singh
2021-08-25 19:19   ` Borislav Petkov
2021-08-27 16:46     ` Michael Roth
2021-08-31 10:04       ` Borislav Petkov
2021-09-01  1:03         ` Michael Roth
2021-09-02 10:53           ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 29/38] x86/boot: add a pointer to Confidential Computing blob in bootparams Brijesh Singh
2021-08-27 13:51   ` Borislav Petkov
2021-08-27 18:48     ` Michael Roth
2021-08-20 15:19 ` [PATCH Part1 v5 30/38] x86/compressed/64: store Confidential Computing blob address " Brijesh Singh
2021-08-27 14:15   ` Borislav Petkov
2021-08-27 19:09     ` Michael Roth
2021-08-31 10:26       ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 31/38] x86/compressed/64: add identity mapping for Confidential Computing blob Brijesh Singh
2021-08-27 14:43   ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 32/38] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers Brijesh Singh
2021-08-27 15:18   ` Borislav Petkov
2021-08-27 15:47     ` Brijesh Singh
2021-08-27 16:56       ` Borislav Petkov
2021-08-27 18:39       ` Michael Roth
2021-08-27 18:32     ` Michael Roth
2021-08-30 16:03       ` Michael Roth
2021-08-31 16:22       ` Borislav Petkov
2021-09-01  1:16         ` Michael Roth
2021-09-02 11:05           ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 33/38] x86/sev: Provide support for SNP guest request NAEs Brijesh Singh
2021-08-27 17:44   ` Borislav Petkov
2021-08-27 18:07     ` Brijesh Singh
2021-08-27 18:13       ` Borislav Petkov
2021-08-27 18:27         ` Brijesh Singh
2021-08-27 18:38           ` Borislav Petkov
2021-08-27 19:57       ` Tom Lendacky
2021-08-27 20:17         ` Borislav Petkov
2021-08-27 20:31           ` Tom Lendacky
2021-08-20 15:19 ` [PATCH Part1 v5 34/38] x86/sev: Add snp_msg_seqno() helper Brijesh Singh
2021-08-27 18:41   ` Borislav Petkov
2021-08-30 15:07     ` Brijesh Singh
2021-09-02 11:26       ` Borislav Petkov
2021-09-02 15:27         ` Brijesh Singh
2021-08-31 20:46   ` Dov Murik
2021-08-31 21:13     ` Brijesh Singh
2021-09-09 14:54   ` Peter Gonda
2021-09-09 15:26     ` Brijesh Singh
2021-09-09 15:43       ` Peter Gonda
2021-09-09 16:17         ` Brijesh Singh
2021-09-09 16:21           ` Peter Gonda
2021-09-09 19:26             ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 35/38] x86/sev: Register SNP guest request platform device Brijesh Singh
2021-08-31 11:37   ` Dov Murik
2021-08-31 16:03     ` Brijesh Singh
2021-09-02 16:40   ` Borislav Petkov
2021-09-02 19:58     ` Brijesh Singh
2021-09-03  8:15       ` Dov Murik
2021-09-03 12:08         ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 36/38] virt: Add SEV-SNP guest driver Brijesh Singh
2021-09-06 17:38   ` Borislav Petkov
2021-09-07 13:35     ` Brijesh Singh
2021-09-08 13:44       ` Borislav Petkov
2021-08-20 15:19 ` [PATCH Part1 v5 37/38] virt: sevguest: Add support to derive key Brijesh Singh
2021-08-31 18:59   ` Dov Murik
2021-08-31 21:04     ` Brijesh Singh
2021-09-01  5:33       ` Dov Murik
2021-09-08 14:00   ` Borislav Petkov
2021-09-08 21:44     ` Brijesh Singh
2021-08-20 15:19 ` [PATCH Part1 v5 38/38] virt: sevguest: Add support to get extended report Brijesh Singh
2021-08-31 20:22   ` Dov Murik
2021-08-31 21:11     ` Brijesh Singh
2021-09-01  8:32       ` Dov Murik
2021-09-08 17:53   ` Borislav Petkov
2021-09-15 11:46     ` Brijesh Singh
2021-09-15 10:02   ` Dr. David Alan Gilbert
2021-09-15 11:53     ` Brijesh Singh

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