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Subject[PATCH] 1-access_process_vm_user
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This patch modifies the functions ptrace_readdata and
ptrace_writedata already included in kernel/ptrace.c. Basically this is a more
efficient implementation of the same features.
A third function ptrace_readstringdata has been added to optimize the data
transfer of null terminated char strings (like pathnames).

A new function, access_process_vm_user(), takes care to get data from userspace
memory of a given process or to write to userspace memory, in a similar way of
the already existent access_process_vm() function.
It uses only an additional parameter: the flag "string" specify if making
checks on data, that should be a well-formed string ( null terminated ):

static int access_process_vm_user(struct task_struct *tsk, unsigned long addr, char __user *ubuf, int len, int write, int string)

We think this is a better implementation of readdata and writedata, because it
retains in cache entire memory pages, while the current implementation uses only
128 bytes buffers.

Signed-off-by: renzo davoli <renzo@cs.unibo.it>

diff -Naur linux-2.6.17-rc1-bulk/include/linux/ptrace.h linux-2.6.17-rc1-access/include/linux/ptrace.h
--- linux-2.6.17-rc1-bulk/include/linux/ptrace.h 2006-04-03 05:22:10.000000000 +0200
+++ linux-2.6.17-rc1-access/include/linux/ptrace.h 2006-04-04 10:01:33.000000000 +0200
@@ -81,6 +81,7 @@
extern struct task_struct *ptrace_get_task_struct(pid_t pid);
extern int ptrace_traceme(void);
extern int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len);
+extern int ptrace_readstringdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len);
extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len);
extern int ptrace_attach(struct task_struct *tsk);
extern int ptrace_detach(struct task_struct *, unsigned int);
diff -Naur linux-2.6.17-rc1-bulk/kernel/ptrace.c linux-2.6.17-rc1-access/kernel/ptrace.c
--- linux-2.6.17-rc1-bulk/kernel/ptrace.c 2006-04-03 05:22:10.000000000 +0200
+++ linux-2.6.17-rc1-access/kernel/ptrace.c 2006-04-04 10:01:33.000000000 +0200
@@ -263,54 +263,90 @@
return buf - old_buf;
}

-int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
+/*
+ * Access another process' address space to/from user space
+ * Do not walk the page table directly, use get_user_pages
+ */
+static int access_process_vm_user(struct task_struct *tsk, unsigned long addr, char __user *ubuf, int len, int write, int string)
{
- int copied = 0;
-
- while (len > 0) {
- char buf[128];
- int this_len, retval;
-
- this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
- retval = access_process_vm(tsk, src, buf, this_len, 0);
- if (!retval) {
- if (copied)
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ struct page *page;
+ char *buf;
+ unsigned long old_addr = addr;
+
+ mm = get_task_mm(tsk);
+ if (!mm)
+ return 0;
+
+ buf=kmalloc(PAGE_SIZE, GFP_KERNEL);
+ down_read(&mm->mmap_sem);
+ /* ignore errors, just check how much was sucessfully transfered */
+ while (len) {
+ int bytes, ret, offset;
+ void *maddr;
+
+ ret = get_user_pages(tsk, mm, addr, 1,
+ write, 1, &page, &vma);
+ if (ret <= 0)
break;
- return -EIO;
+
+ bytes = len;
+ offset = addr & (PAGE_SIZE-1);
+ if (bytes > PAGE_SIZE-offset)
+ bytes = PAGE_SIZE-offset;
+
+ maddr = kmap(page);
+ if (write) {
+ __copy_from_user(buf,ubuf,bytes);
+ copy_to_user_page(vma, page, addr,
+ maddr + offset, buf, bytes);
+ if (!PageCompound(page))
+ set_page_dirty_lock(page);
+ } else {
+ copy_from_user_page(vma, page, addr,
+ buf, maddr + offset, bytes);
+ if (string) {
+ for (offset=0;offset<bytes;offset++)
+ if (buf[offset]==0)
+ break;
+ if (offset < bytes)
+ bytes=len=offset+1;
}
- if (copy_to_user(dst, buf, retval))
- return -EFAULT;
- copied += retval;
- src += retval;
- dst += retval;
- len -= retval;
+ __copy_to_user(ubuf,buf,bytes);
}
- return copied;
+ kunmap(page);
+ page_cache_release(page);
+ len -= bytes;
+ ubuf += bytes;
+ addr += bytes;
}
+ up_read(&mm->mmap_sem);
+ mmput(mm);

-int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
-{
- int copied = 0;
+ kfree(buf);
+ return addr - old_addr;
+}

- while (len > 0) {
- char buf[128];
- int this_len, retval;
-
- this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
- if (copy_from_user(buf, src, this_len))
- return -EFAULT;
- retval = access_process_vm(tsk, dst, buf, this_len, 1);
- if (!retval) {
- if (copied)
- break;
+int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
+{
+ if (!access_ok(VERIFY_WRITE, dst ,len))
return -EIO;
+ return access_process_vm_user(tsk, src, dst, len, 0, 0);
}
- copied += retval;
- src += retval;
- dst += retval;
- len -= retval;
+
+int ptrace_readstringdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
+{
+ if (!access_ok(VERIFY_WRITE, dst ,len))
+ return -EIO;
+ return access_process_vm_user(tsk, src, dst, len, 0, 1);
}
- return copied;
+
+int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
+{
+ if (!access_ok(VERIFY_READ, dst ,len))
+ return -EIO;
+ return access_process_vm_user(tsk, dst, src, len, 1, 0);
}

static int ptrace_setoptions(struct task_struct *child, long data)
-
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