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authorFrans Kaashoek <[email protected]>2016-08-26 08:46:13 -0400
committerFrans Kaashoek <[email protected]>2016-08-26 08:46:13 -0400
commit37939f24c2fbb12a57a628fedd024a4865741e74 (patch)
tree60693dc51ec3d332b09fd19840b467d7b2cca283 /vm.c
parent27ff70dc083b650c5c44d5145c2991f32d8ff547 (diff)
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Diffstat (limited to 'vm.c')
-rw-r--r--vm.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/vm.c b/vm.c
index d4982ee..c8b8d35 100644
--- a/vm.c
+++ b/vm.c
@@ -168,7 +168,9 @@ switchuvm(struct proc *p)
cpu->gdt[SEG_TSS].s = 0;
cpu->ts.ss0 = SEG_KDATA << 3;
cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE;
- cpu->ts.iomb = (ushort) 0xFFFF; // forbid I/O instructions from user space
+ // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit
+ // forbids I/O instructions (e.g., inb and outb) from user space
+ cpu->ts.iomb = (ushort) 0xFFFF;
ltr(SEG_TSS << 3);
if(p->pgdir == 0)
panic("switchuvm: no pgdir");