lguest: switch segment-voodoo-numbers to readable symbols
When studying lguest's x86 segment descriptor code, it is not longer
necessary to have the Intel x86 architecture manual open on the page
with the segment descriptor illustration to understand the crazy
numbers assigned to both descriptor structure halves a/b.
Now the struct desc_struct's fields, like suggested by
Glauber de Oliveira Costa in 2008, are used.
Signed-off-by: Jacek Galowicz <jacek@galowicz.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c
index ede4658..c4fb424 100644
--- a/drivers/lguest/segments.c
+++ b/drivers/lguest/segments.c
@@ -81,8 +81,8 @@
* sometimes careless and leaves this as 0, even though it's
* running at privilege level 1. If so, we fix it here.
*/
- if ((cpu->arch.gdt[i].b & 0x00006000) == 0)
- cpu->arch.gdt[i].b |= (GUEST_PL << 13);
+ if (cpu->arch.gdt[i].dpl == 0)
+ cpu->arch.gdt[i].dpl |= GUEST_PL;
/*
* Each descriptor has an "accessed" bit. If we don't set it
@@ -90,7 +90,7 @@
* that entry into a segment register. But the GDT isn't
* writable by the Guest, so bad things can happen.
*/
- cpu->arch.gdt[i].b |= 0x00000100;
+ cpu->arch.gdt[i].type |= 0x1;
}
}
@@ -114,13 +114,19 @@
/*
* The TSS segment refers to the TSS entry for this particular CPU.
- * Forgive the magic flags: the 0x8900 means the entry is Present, it's
- * privilege level 0 Available 386 TSS system segment, and the 0x67
- * means Saturn is eclipsed by Mercury in the twelfth house.
*/
- gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16);
- gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000)
- | ((tss >> 16) & 0x000000FF);
+ gdt[GDT_ENTRY_TSS].a = 0;
+ gdt[GDT_ENTRY_TSS].b = 0;
+
+ gdt[GDT_ENTRY_TSS].limit0 = 0x67;
+ gdt[GDT_ENTRY_TSS].base0 = tss & 0xFFFF;
+ gdt[GDT_ENTRY_TSS].base1 = (tss >> 16) & 0xFF;
+ gdt[GDT_ENTRY_TSS].base2 = tss >> 24;
+ gdt[GDT_ENTRY_TSS].type = 0x9; /* 32-bit TSS (available) */
+ gdt[GDT_ENTRY_TSS].p = 0x1; /* Entry is present */
+ gdt[GDT_ENTRY_TSS].dpl = 0x0; /* Privilege level 0 */
+ gdt[GDT_ENTRY_TSS].s = 0x0; /* system segment */
+
}
/*
@@ -135,8 +141,8 @@
*/
cpu->arch.gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT;
cpu->arch.gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT;
- cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13);
- cpu->arch.gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13);
+ cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].dpl |= GUEST_PL;
+ cpu->arch.gdt[GDT_ENTRY_KERNEL_DS].dpl |= GUEST_PL;
}
/*H:650