Imbus/xv6-riscv-kernel
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Compile user binary to map text without W and data without X

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Use the flags in elf header to set vm permissions
Modify pgbug() so that usertests text segment is without W
Add test to check app cannot write text segment
This commit is contained in:
Frans Kaashoek 2022-08-15 19:02:19 -04:00
parent 2175c6b0b6
commit cef1b57d4a
3 changed files with 49 additions and 11 deletions
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27
kernel/exec.c
View file

@ -7,7 +7,17 @@
#include "defs.h"
#include "elf.h"
static int loadseg(pde_t *pgdir, uint64 addr, struct inode *ip, uint offset, uint sz);
static int loadseg(pde_t *, uint64, uint, struct inode *, uint, uint);
int flags2perm(int flags)
{
int perm = 0;
if(flags & 0x1)
perm = PTE_X;
if(flags & 0x2)
perm |= PTE_W;
return perm;
}
int
exec(char *path, char **argv)
@ -32,6 +42,7 @@ exec(char *path, char **argv)
// Check ELF header
if(readi(ip, 0, (uint64)&elf, 0, sizeof(elf)) != sizeof(elf))
goto bad;
if(elf.magic != ELF_MAGIC)
goto bad;
@ -48,13 +59,15 @@ exec(char *path, char **argv)
goto bad;
if(ph.vaddr + ph.memsz < ph.vaddr)
goto bad;
if(ph.align != PGSIZE)
goto bad;
uint64 e = PGROUNDUP(ph.vaddr + ph.memsz);
uint64 sz1;
if((sz1 = uvmalloc(pagetable, sz, ph.vaddr + ph.memsz, PTE_X|PTE_W)) == 0)
if((sz1 = uvmalloc(pagetable, sz, e, flags2perm(ph.flags))) == 0)
goto bad;
sz = sz1;
if((ph.vaddr % PGSIZE) != 0)
goto bad;
if(loadseg(pagetable, ph.vaddr, ip, ph.off, ph.filesz) < 0)
uint64 s = PGROUNDDOWN(ph.vaddr);
if(loadseg(pagetable, s, ph.vaddr - s, ip, ph.off, ph.filesz) < 0)
goto bad;
}
iunlockput(ip);
@ -134,7 +147,7 @@ exec(char *path, char **argv)
// and the pages from va to va+sz must already be mapped.
// Returns 0 on success, -1 on failure.
static int
loadseg(pagetable_t pagetable, uint64 va, struct inode *ip, uint offset, uint sz)
loadseg(pagetable_t pagetable, uint64 va, uint poff, struct inode *ip, uint offset, uint sz)
{
uint i, n;
uint64 pa;
@ -147,7 +160,7 @@ loadseg(pagetable_t pagetable, uint64 va, struct inode *ip, uint offset, uint sz
n = sz - i;
else
n = PGSIZE;
if(readi(ip, 0, (uint64)pa, offset+i, n) != n)
if(readi(ip, 0, (uint64)pa+poff, offset+i, n) != n)
return -1;
}