d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
79 lines
1.8 KiB
C
79 lines
1.8 KiB
C
// User-memory access helpers — see include/uaccess.h for the rules.
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//
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// Everything here validates against the *current* process's page table
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// (myproc()->pgdir), which is also the live CR3 while a syscall runs, so a
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// range that passes access_ok() can be dereferenced directly by kernel
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// code for the remainder of the syscall (single-threaded processes can't
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// unmap it out from under us mid-call).
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#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "memlayout.h"
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#include "mmu.h"
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#include "proc.h"
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#include "errno.h"
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#include "uaccess.h"
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int
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access_ok(addr_t uaddr, uint64 size)
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{
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addr_t a, end;
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if(size == 0)
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return 1;
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end = uaddr + size;
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if(end < uaddr || end > KERNBASE)
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return 0;
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for(a = PGROUNDDOWN(uaddr); a < end; a += PGSIZE)
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if(uva2ka(myproc()->pgdir, (char*)a) == 0)
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return 0;
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return 1;
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}
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void*
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user_ptr(addr_t uaddr, uint64 size)
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{
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if(uaddr == 0 || !access_ok(uaddr, size))
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return 0;
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return (void*)uaddr;
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}
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int
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copy_from_user(void *dst, addr_t uaddr, uint64 n)
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{
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if(uaddr + n < uaddr || uaddr + n > KERNBASE)
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return -EFAULT;
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if(copyin(myproc()->pgdir, uaddr, dst, n) < 0)
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return -EFAULT;
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return 0;
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}
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int
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copy_to_user(addr_t uaddr, const void *src, uint64 n)
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{
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if(uaddr + n < uaddr || uaddr + n > KERNBASE)
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return -EFAULT;
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if(copyout(myproc()->pgdir, uaddr, (void*)src, n) < 0)
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return -EFAULT;
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return 0;
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}
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long
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strlen_user(addr_t uaddr)
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{
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addr_t a = uaddr;
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while(a - uaddr < USER_STR_MAX){
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// Scan through the per-page kernel alias so an unmapped page is a
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// clean failure instead of a fault.
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char *ka = uva2ka(myproc()->pgdir, (char*)a);
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if(ka == 0)
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return -EFAULT;
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addr_t pgend = PGROUNDDOWN(a) + PGSIZE;
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for(; a < pgend; a++, ka++)
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if(*ka == 0)
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return a - uaddr;
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}
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return -EFAULT;
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}
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