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SubjectRe: [PATCH 08/62] x86/boot/compressed/64: Add IDT Infrastructure
On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@8bytes.org> wrote:
>
> From: Joerg Roedel <jroedel@suse.de>
>
> Add code needed to setup an IDT in the early pre-decompression
> boot-code. The IDT is loaded first in startup_64, which is after
> EfiExitBootServices() has been called, and later reloaded when the
> kernel image has been relocated to the end of the decompression area.
>
> This allows to setup different IDT handlers before and after the
> relocation.
>

> diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
> new file mode 100644
> index 000000000000..46ecea671b90
> --- /dev/null
> +++ b/arch/x86/boot/compressed/idt_64.c
> @@ -0,0 +1,43 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <asm/trap_defs.h>
> +#include <asm/segment.h>
> +#include "misc.h"
> +
> +static void set_idt_entry(int vector, void (*handler)(void))
> +{
> + unsigned long address = (unsigned long)handler;
> + gate_desc entry;
> +
> + memset(&entry, 0, sizeof(entry));
> +
> + entry.offset_low = (u16)(address & 0xffff);
> + entry.segment = __KERNEL_CS;
> + entry.bits.type = GATE_TRAP;

^^^

I realize we're not running a real kernel here, but GATE_TRAP is
madness. Please use GATE_INTERRUPT.

> + entry.bits.p = 1;
> + entry.offset_middle = (u16)((address >> 16) & 0xffff);
> + entry.offset_high = (u32)(address >> 32);
> +
> + memcpy(&boot_idt[vector], &entry, sizeof(entry));
> +}
> +
> +/* Have this here so we don't need to include <asm/desc.h> */
> +static void load_boot_idt(const struct desc_ptr *dtr)
> +{
> + asm volatile("lidt %0"::"m" (*dtr));
> +}
> +
> +/* Setup IDT before kernel jumping to .Lrelocated */
> +void load_stage1_idt(void)
> +{
> + boot_idt_desc.address = (unsigned long)boot_idt;
> +
> + load_boot_idt(&boot_idt_desc);
> +}
> +
> +/* Setup IDT after kernel jumping to .Lrelocated */
> +void load_stage2_idt(void)
> +{
> + boot_idt_desc.address = (unsigned long)boot_idt;
> +
> + load_boot_idt(&boot_idt_desc);
> +}
> diff --git a/arch/x86/boot/compressed/idt_handlers_64.S b/arch/x86/boot/compressed/idt_handlers_64.S
> new file mode 100644
> index 000000000000..0b2b6cf747d2
> --- /dev/null
> +++ b/arch/x86/boot/compressed/idt_handlers_64.S
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Early IDT handler entry points
> + *
> + * Copyright (C) 2019 SUSE
> + *
> + * Author: Joerg Roedel <jroedel@suse.de>
> + */
> +
> +#include <asm/segment.h>
> +
> +.macro EXCEPTION_HANDLER name function error_code=0
> +SYM_FUNC_START(\name)
> +
> + /* Build pt_regs */
> + .if \error_code == 0
> + pushq $0
> + .endif

cld

> +
> + pushq %rdi
> + pushq %rsi
> + pushq %rdx
> + pushq %rcx
> + pushq %rax
> + pushq %r8
> + pushq %r9
> + pushq %r10
> + pushq %r11
> + pushq %rbx
> + pushq %rbp
> + pushq %r12
> + pushq %r13
> + pushq %r14
> + pushq %r15
> +
> + /* Call handler with pt_regs */
> + movq %rsp, %rdi
> + call \function
> +
> + /* Restore regs */
> + popq %r15
> + popq %r14
> + popq %r13
> + popq %r12
> + popq %rbp
> + popq %rbx
> + popq %r11
> + popq %r10
> + popq %r9
> + popq %r8
> + popq %rax
> + popq %rcx
> + popq %rdx
> + popq %rsi
> + popq %rdi

if error_code?

> +
> + /* Remove error code and return */
> + addq $8, %rsp
> +
> + /*
> + * Make sure we return to __KERNEL_CS - the CS selector on
> + * the IRET frame might still be from an old BIOS GDT
> + */
> + movq $__KERNEL_CS, 8(%rsp)
> +

If this actually happens, you have a major bug. Please sanitize all
the segment registers after installing the GDT rather than hacking
around it here.

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