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overkill: use segments to catch stack overflow (delete before next year)

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rsc 2007-09-27 19:39:10 +00:00
parent 8c8b748a2f
commit 39c3fb1b15
3 changed files with 13 additions and 2 deletions
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6
proc.c
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@ -73,7 +73,7 @@ setupsegs(struct proc *p)
splhi();
c = &cpus[cpu()];
c->ts.ss0 = SEG_KDATA << 3;
c->ts.ss0 = SEG_PROCSTACK << 3;
if(p)
c->ts.esp0 = (uint)(p->kstack + KSTACKSIZE);
else
@ -84,12 +84,15 @@ setupsegs(struct proc *p)
c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint)&c->ts, sizeof(c->ts)-1, 0);
c->gdt[SEG_TSS].s = 0;
c->gdt[SEG_CPUSTACK] = SEG(STA_W|STA_E, 0, (uint)c->stack, 0);
if(p){
c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)p->mem, p->sz-1, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, (uint)p->mem, p->sz-1, DPL_USER);
c->gdt[SEG_PROCSTACK] = SEG(STA_W|STA_E, 0, (uint)p->kstack, 0);
} else {
c->gdt[SEG_UCODE] = SEG_NULL;
c->gdt[SEG_UDATA] = SEG_NULL;
c->gdt[SEG_PROCSTACK] = SEG_NULL;
}
lgdt(c->gdt, sizeof(c->gdt));
@ -140,6 +143,7 @@ copyproc(struct proc *p)
memset(&np->context, 0, sizeof(np->context));
np->context.eip = (uint)forkret;
np->context.esp = (uint)np->tf;
np->context.ss = SEG_PROCSTACK<<3;
// Clear %eax so that fork system call returns 0 in child.
np->tf->eax = 0;

5
proc.h
View file

@ -4,7 +4,9 @@
#define SEG_UCODE 3
#define SEG_UDATA 4
#define SEG_TSS 5 // this process's task state
#define NSEGS 6
#define SEG_CPUSTACK 6
#define SEG_PROCSTACK 7
#define NSEGS 8
// Saved registers for kernel context switches.
// Don't need to save all the %fs etc. segment registers,
@ -22,6 +24,7 @@ struct context {
int esi;
int edi;
int ebp;
int ss;
};
enum proc_state { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };

4
swtch.S
View file

@ -16,10 +16,14 @@ swtch:
movl %esi, 20(%eax)
movl %edi, 24(%eax)
movl %ebp, 28(%eax)
movl %ss, %ebx
movl %ebx, 32(%eax)
# Load new registers
movl 4(%esp), %eax # not 8(%esp) - popped return address above
movl 32(%eax), %ebx
movl %ebx, %ss
movl 28(%eax), %ebp
movl 24(%eax), %edi
movl 20(%eax), %esi