Compile user binary to map text without W and data without X

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

1 files changed, 20 insertions, 7 deletions

diff --git a/kernel/exec.c b/kernel/exec.c
index 3c468e1..aee9345 100644
--- a/kernel/exec.c
+++ b/kernel/exec.c
@@ -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;
   }