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u2mfn: get mfn via pte

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Before this commit u2mfn got the address via kmap(get_user_pages(...)).
This has the problem that get_user_pages() does not work in some cases.
For example when qemu in a stubdom tries to get the mfn for a page which
is mapped from the target domain u2mfn fails because get_user_pages()
cannot be used for such mappings.

So get the address from the pte with apply_to_page_range(). Since we are
only interested in one page get_locked_pte() would be simpler but it's
not available to modules.
This commit is contained in:
HW42 2017-07-05 20:21:22 +02:00 committed by Simon Gaiser
parent 7458893b8f
commit 7e6bee6281
1 changed files with 13 additions and 20 deletions
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33
kernel-modules/u2mfn/u2mfn.c
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@ -54,6 +54,11 @@ static inline unsigned long VIRT_TO_MFN(void *addr)
}
#endif
static int u2mfn_get_mfn(pte_t *pte, pgtable_t token, unsigned long addr, void *data) {
*((unsigned long *) data) = pfn_to_mfn(pte_pfn(*pte));
return 0;
}
/// User virtual address to mfn translator
/**
\param cmd ignored
@ -63,9 +68,8 @@ static inline unsigned long VIRT_TO_MFN(void *addr)
static long u2mfn_ioctl(struct file *f, unsigned int cmd,
unsigned long data)
{
struct page *user_page;
void *kaddr;
long ret;
unsigned long mfn;
if (_IOC_TYPE(cmd) != U2MFN_MAGIC) {
printk("Qubes u2mfn: wrong IOCTL magic");
@ -74,26 +78,15 @@ static long u2mfn_ioctl(struct file *f, unsigned int cmd,
switch (cmd) {
case U2MFN_GET_MFN_FOR_PAGE:
down_read(&current->mm->mmap_sem);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 9, 0)
ret = get_user_pages
(data, 1, (FOLL_WRITE | FOLL_FORCE), &user_page, 0);
#elif LINUX_VERSION_CODE >= KERNEL_VERSION(4, 6, 0)
ret = get_user_pages
(data, 1, 1, 0, &user_page, 0);
#else
ret = get_user_pages
(current, current->mm, data, 1, 1, 0, &user_page, 0);
#endif
up_read(&current->mm->mmap_sem);
if (ret != 1) {
printk("U2MFN_GET_MFN_FOR_PAGE: get_user_pages failed, ret=0x%lx\n", ret);
ret = apply_to_page_range(current->mm, data, PAGE_SIZE, u2mfn_get_mfn, &mfn);
if (ret < 0 || mfn == INVALID_P2M_ENTRY) {
printk("U2MFN_GET_MFN_FOR_PAGE: failed to get mfn, "
"addr=0x%lx ret=0x%lx\n", data, ret);
return -1;
}
kaddr = kmap(user_page);
ret = VIRT_TO_MFN(kaddr);
kunmap(user_page);
put_page(user_page);
ret = mfn;
break;
case U2MFN_GET_LAST_MFN: