linux-kernel - [PATCH v3 31/75] x86/head/64: Install boot GDT

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Message-Id: <20200428151725.31091-32-joro@8bytes.org>
Date:   Tue, 28 Apr 2020 17:16:41 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v3 31/75] x86/head/64: Install boot GDT

From: Joerg Roedel <jroedel@...e.de>

Handling exceptions during boot requires a working GDT. The kernel GDT
is not yet ready for use, so install a temporary boot GDT.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/head_64.S | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4bbc770af632..11a28c1fb51f 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -72,6 +72,26 @@ SYM_CODE_START_NOALIGN(startup_64)
 	/* Set up the stack for verify_cpu(), similar to initial_stack below */
 	leaq	(__end_init_task - SIZEOF_PTREGS)(%rip), %rsp
 
+	/* Setup boot GDT descriptor and load boot GDT */
+	leaq	boot_gdt(%rip), %rax
+	movq	%rax, boot_gdt_base(%rip)
+	lgdt	boot_gdt_descr(%rip)
+
+	/* New GDT is live - reload data segment registers */
+	movl	$__KERNEL_DS, %eax
+	movl	%eax, %ds
+	movl	%eax, %ss
+	movl	%eax, %es
+
+	/* Now switch to __KERNEL_CS so IRET works reliably */
+	pushq	$__KERNEL_CS
+	leaq	.Lon_kernel_cs(%rip), %rax
+	pushq	%rax
+	lretq
+
+.Lon_kernel_cs:
+	UNWIND_HINT_EMPTY
+
 	/* Sanitize CPU configuration */
 	call verify_cpu
 
@@ -480,6 +500,22 @@ SYM_DATA_LOCAL(early_gdt_descr_base,	.quad INIT_PER_CPU_VAR(gdt_page))
 SYM_DATA(phys_base, .quad 0x0)
 EXPORT_SYMBOL(phys_base)
 
+/* Boot GDT used when kernel addresses are not mapped yet */
+SYM_DATA_LOCAL(boot_gdt_descr,		.word boot_gdt_end - boot_gdt)
+SYM_DATA_LOCAL(boot_gdt_base,		.quad 0)
+SYM_DATA_START(boot_gdt)
+	.quad	0
+	.quad   0x00cf9a000000ffff	/* __KERNEL32_CS */
+	.quad   0x00af9a000000ffff	/* __KERNEL_CS */
+	.quad   0x00cf92000000ffff	/* __KERNEL_DS */
+	.quad	0			/* __USER32_CS - unused */
+	.quad	0			/* __USER_DS   - unused */
+	.quad	0			/* __USER_CS   - unused */
+	.quad	0			/* unused */
+	.quad   0x0080890000000000	/* TSS descriptor */
+	.quad   0x0000000000000000	/* TSS continued */
+SYM_DATA_END_LABEL(boot_gdt, SYM_L_LOCAL, boot_gdt_end)
+
 #include "../../x86/xen/xen-head.S"
 
 	__PAGE_ALIGNED_BSS
-- 
2.17.1