Isaku Yamahata
2007-Aug-14 09:50 UTC
[Xen-devel] [PATCH 3/7] xencomm take 3: xen side fix invalid or racy access
# HG changeset patch
# User yamahata@valinux.co.jp
# Date 1187079421 -32400
# Node ID cf7a9141e7f884a14cfab8d3785c95dea85749be
# Parent 4dbbedee6bb8d594287940470a61b8c0c56daf9c
[xen, xencomm] fix various xencomm invalid racy access.
- Xencomm should check struct xencomm_desc alignment.
- Xencomm should check whether struct xencomm_desc itself (8 bytes)
doesn''t
cross page boundary. Otherwise a hostile guest kernel can pass such
a pointer that may across page boundary. Then xencomm accesses a unrelated
page.
- Xencomm shouldn''t access struct xencomm_desc::nr_addrs multiple
times.
Copy it to local area and use the copy.
Otherwise a hostile guest can modify at the same time.
- Xencomm should check whether struct xencomm_desc::address[] array crosses
page boundary. Otherwise xencomm may access unrelated pages.
- Xencomm should get_page()/put_page() after address conversion from paddr
to maddr because xen supports SMP and balloon driver.
Otherwise another vcpu may free the page at the same time.
Such a domain behaviour doesn''t make sense, however nothing prevents
it.
PATCHNAME: fix_xencomm_invalid_racy_access
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
diff -r 4dbbedee6bb8 -r cf7a9141e7f8 xen/common/xencomm.c
--- a/xen/common/xencomm.c Tue Aug 14 16:46:23 2007 +0900
+++ b/xen/common/xencomm.c Tue Aug 14 17:17:01 2007 +0900
@@ -35,12 +35,149 @@ static int xencomm_debug = 1; /* extreme
#endif
static void*
-xencomm_maddr_to_vaddr(unsigned long maddr)
-{
+xencomm_vaddr(unsigned long paddr, struct page_info *page)
+{
+ return (void*)((paddr & ~PAGE_MASK) | (unsigned
long)page_to_virt(page));
+}
+
+/* get_page() to prevent from another vcpu freeing the page */
+static int
+xencomm_get_page(unsigned long paddr, struct page_info **page)
+{
+ unsigned long maddr = paddr_to_maddr(paddr);
if (maddr == 0)
- return NULL;
-
- return maddr_to_virt(maddr);
+ return -EFAULT;
+
+ *page = maddr_to_page(maddr);
+ if (get_page(*page, current->domain) == 0) {
+ if (page_get_owner(*page) != current->domain) {
+ /*
+ * This page might be a page granted by another domain, or
+ * this page is freed with decrease reservation hypercall at
+ * the same time.
+ */
+ gdprintk(XENLOG_WARNING,
+ "bad page is passed. paddr 0x%lx maddr 0x%lx\n",
+ paddr, maddr);
+ return -EFAULT;
+ }
+
+ /* Try again. */
+ cpu_relax();
+ return -EAGAIN;
+ }
+
+ return 0;
+}
+
+/* check if struct desc doesn''t cross page boundry */
+static int
+xencomm_desc_cross_page_boundary(unsigned long paddr)
+{
+ unsigned long offset = paddr & ~PAGE_MASK;
+ if (offset > PAGE_SIZE - sizeof(struct xencomm_desc))
+ return 1;
+ return 0;
+}
+
+struct xencomm_ctxt {
+ struct xencomm_desc *desc;
+
+ uint32_t nr_addrs;
+ struct page_info *page;
+};
+
+static uint32_t
+xencomm_ctxt_nr_addrs(const struct xencomm_ctxt *ctxt)
+{
+ return ctxt->nr_addrs;
+}
+
+static unsigned long*
+xencomm_ctxt_address(struct xencomm_ctxt *ctxt, int i)
+{
+ return &ctxt->desc->address[i];
+}
+
+/* check if struct xencomm_desc and address array cross page boundary */
+static int
+xencomm_ctxt_cross_page_boundary(struct xencomm_ctxt *ctxt)
+{
+ unsigned long saddr = (unsigned long)ctxt->desc;
+ unsigned long eaddr + (unsigned
long)&ctxt->desc->address[ctxt->nr_addrs] - 1;
+ if ((saddr >> PAGE_SHIFT) != (eaddr >> PAGE_SHIFT))
+ return 1;
+ return 0;
+}
+
+static int
+xencomm_ctxt_init(const void* handle, struct xencomm_ctxt *ctxt)
+{
+ struct page_info *page;
+ struct xencomm_desc *desc;
+ int ret;
+
+ /* avoid unaligned access */
+ if ((unsigned long)handle % __alignof__(*desc) != 0)
+ return -EINVAL;
+ if (xencomm_desc_cross_page_boundary((unsigned long)handle))
+ return -EINVAL;
+
+ /* first we need to access the descriptor */
+ ret = xencomm_get_page((unsigned long)handle, &page);
+ if (ret)
+ return ret;
+
+ desc = xencomm_vaddr((unsigned long)handle, page);
+ if (desc->magic != XENCOMM_MAGIC) {
+ printk("%s: error: %p magic was 0x%x\n", __func__, desc,
desc->magic);
+ put_page(page);
+ return -EINVAL;
+ }
+
+ ctxt->desc = desc;
+ ctxt->nr_addrs = desc->nr_addrs; /* copy before use.
+ * It is possible for a guest domain to
+ * modify concurrently.
+ */
+ ctxt->page = page;
+ if (xencomm_ctxt_cross_page_boundary(ctxt)) {
+ put_page(page);
+ return -EINVAL;
+ }
+ return 0;
+}
+
+static void
+xencomm_ctxt_done(struct xencomm_ctxt *ctxt)
+{
+ put_page(ctxt->page);
+}
+
+static int
+xencomm_copy_chunk_from(unsigned long to, unsigned long paddr,
+ unsigned int len)
+{
+ struct page_info *page;
+
+ while (1) {
+ int res;
+ res = xencomm_get_page(paddr, &page);
+ if (res != 0) {
+ if (res == -EAGAIN)
+ continue; /* Try again. */
+ return res;
+ }
+ if (xencomm_debug)
+ printk("%lx[%d] -> %lx\n",
+ (unsigned long)xencomm_vaddr(paddr, page), len, to);
+
+ memcpy((void *)to, xencomm_vaddr(paddr, page), len);
+ put_page(page);
+ return 0;
+ }
+ /* NOTREACHED */
}
static unsigned long
@@ -53,17 +190,14 @@ xencomm_inline_from_guest(void *to, cons
while (n > 0) {
unsigned int chunksz;
- unsigned long src_maddr;
unsigned int bytes;
chunksz = PAGE_SIZE - (src_paddr % PAGE_SIZE);
bytes = min(chunksz, n);
- src_maddr = paddr_to_maddr(src_paddr);
- if (xencomm_debug)
- printk("%lx[%d] -> %lx\n", src_maddr, bytes, (unsigned
long)to);
- memcpy(to, maddr_to_virt(src_maddr), bytes);
+ if (xencomm_copy_chunk_from((unsigned long)to, src_paddr, bytes))
+ return n;
src_paddr += bytes;
to += bytes;
n -= bytes;
@@ -89,7 +223,7 @@ xencomm_copy_from_guest(void *to, const
xencomm_copy_from_guest(void *to, const void *from, unsigned int n,
unsigned int skip)
{
- struct xencomm_desc *desc;
+ struct xencomm_ctxt ctxt;
unsigned int from_pos = 0;
unsigned int to_pos = 0;
unsigned int i = 0;
@@ -97,21 +231,12 @@ xencomm_copy_from_guest(void *to, const
if (xencomm_is_inline(from))
return xencomm_inline_from_guest(to, from, n, skip);
- /* first we need to access the descriptor */
- desc = (struct xencomm_desc *)
- xencomm_maddr_to_vaddr(paddr_to_maddr((unsigned long)from));
- if (desc == NULL)
+ if (xencomm_ctxt_init(from, &ctxt))
return n;
- if (desc->magic != XENCOMM_MAGIC) {
- printk("%s: error: %p magic was 0x%x\n",
- __func__, desc, desc->magic);
- return n;
- }
-
/* iterate through the descriptor, copying up to a page at a time */
- while ((to_pos < n) && (i < desc->nr_addrs)) {
- unsigned long src_paddr = desc->address[i];
+ while ((to_pos < n) && (i <
xencomm_ctxt_nr_addrs(&ctxt))) {
+ unsigned long src_paddr = *xencomm_ctxt_address(&ctxt, i);
unsigned int pgoffset;
unsigned int chunksz;
unsigned int chunk_skip;
@@ -130,17 +255,11 @@ xencomm_copy_from_guest(void *to, const
skip -= chunk_skip;
if (skip == 0 && chunksz > 0) {
- unsigned long src_maddr;
- unsigned long dest = (unsigned long)to + to_pos;
unsigned int bytes = min(chunksz, n - to_pos);
- src_maddr = paddr_to_maddr(src_paddr + chunk_skip);
- if (src_maddr == 0)
- return n - to_pos;
-
- if (xencomm_debug)
- printk("%lx[%d] -> %lx\n", src_maddr, bytes,
dest);
- memcpy((void *)dest, maddr_to_virt(src_maddr), bytes);
+ if (xencomm_copy_chunk_from((unsigned long)to + to_pos,
+ src_paddr + chunk_skip, bytes))
+ goto out;
from_pos += bytes;
to_pos += bytes;
}
@@ -148,7 +267,34 @@ xencomm_copy_from_guest(void *to, const
i++;
}
+out:
+ xencomm_ctxt_done(&ctxt);
return n - to_pos;
+}
+
+static int
+xencomm_copy_chunk_to(unsigned long paddr, unsigned long from,
+ unsigned int len)
+{
+ struct page_info *page;
+
+ while (1) {
+ int res;
+ res = xencomm_get_page(paddr, &page);
+ if (res != 0) {
+ if (res == -EAGAIN)
+ continue; /* Try again. */
+ return res;
+ }
+ if (xencomm_debug)
+ printk("%lx[%d] -> %lx\n", from, len,
+ (unsigned long)xencomm_vaddr(paddr, page));
+
+ memcpy(xencomm_vaddr(paddr, page), (void *)from, len);
+ put_page(page);
+ return 0;
+ }
+ /* NOTREACHED */
}
static unsigned long
@@ -161,17 +307,14 @@ xencomm_inline_to_guest(void *to, const
while (n > 0) {
unsigned int chunksz;
- unsigned long dest_maddr;
unsigned int bytes;
chunksz = PAGE_SIZE - (dest_paddr % PAGE_SIZE);
bytes = min(chunksz, n);
- dest_maddr = paddr_to_maddr(dest_paddr);
- if (xencomm_debug)
- printk("%lx[%d] -> %lx\n", (unsigned long)from, bytes,
dest_maddr);
- memcpy(maddr_to_virt(dest_maddr), (void *)from, bytes);
+ if (xencomm_copy_chunk_to(dest_paddr, (unsigned long)from, bytes))
+ return n;
dest_paddr += bytes;
from += bytes;
n -= bytes;
@@ -197,7 +340,7 @@ xencomm_copy_to_guest(void *to, const vo
xencomm_copy_to_guest(void *to, const void *from, unsigned int n,
unsigned int skip)
{
- struct xencomm_desc *desc;
+ struct xencomm_ctxt ctxt;
unsigned int from_pos = 0;
unsigned int to_pos = 0;
unsigned int i = 0;
@@ -205,20 +348,12 @@ xencomm_copy_to_guest(void *to, const vo
if (xencomm_is_inline(to))
return xencomm_inline_to_guest(to, from, n, skip);
- /* first we need to access the descriptor */
- desc = (struct xencomm_desc *)
- xencomm_maddr_to_vaddr(paddr_to_maddr((unsigned long)to));
- if (desc == NULL)
+ if (xencomm_ctxt_init(to, &ctxt))
return n;
- if (desc->magic != XENCOMM_MAGIC) {
- printk("%s error: %p magic was 0x%x\n", __func__, desc,
desc->magic);
- return n;
- }
-
/* iterate through the descriptor, copying up to a page at a time */
- while ((from_pos < n) && (i < desc->nr_addrs)) {
- unsigned long dest_paddr = desc->address[i];
+ while ((from_pos < n) && (i <
xencomm_ctxt_nr_addrs(&ctxt))) {
+ unsigned long dest_paddr = *xencomm_ctxt_address(&ctxt, i);
unsigned int pgoffset;
unsigned int chunksz;
unsigned int chunk_skip;
@@ -237,17 +372,11 @@ xencomm_copy_to_guest(void *to, const vo
skip -= chunk_skip;
if (skip == 0 && chunksz > 0) {
- unsigned long dest_maddr;
- unsigned long source = (unsigned long)from + from_pos;
unsigned int bytes = min(chunksz, n - from_pos);
- dest_maddr = paddr_to_maddr(dest_paddr + chunk_skip);
- if (dest_maddr == 0)
- return n - from_pos;
-
- if (xencomm_debug)
- printk("%lx[%d] -> %lx\n", source, bytes,
dest_maddr);
- memcpy(maddr_to_virt(dest_maddr), (void *)source, bytes);
+ if (xencomm_copy_chunk_to(dest_paddr + chunk_skip,
+ (unsigned long)from + from_pos, bytes))
+ goto out;
from_pos += bytes;
to_pos += bytes;
}
@@ -255,6 +384,8 @@ xencomm_copy_to_guest(void *to, const vo
i++;
}
+out:
+ xencomm_ctxt_done(&ctxt);
return n - from_pos;
}
@@ -268,26 +399,19 @@ static int xencomm_inline_add_offset(voi
* exhausted pages to XENCOMM_INVALID. */
int xencomm_add_offset(void **handle, unsigned int bytes)
{
- struct xencomm_desc *desc;
+ struct xencomm_ctxt ctxt;
int i = 0;
if (xencomm_is_inline(*handle))
return xencomm_inline_add_offset(handle, bytes);
- /* first we need to access the descriptor */
- desc = (struct xencomm_desc *)
- xencomm_maddr_to_vaddr(paddr_to_maddr((unsigned long)*handle));
- if (desc == NULL)
+ if (xencomm_ctxt_init(handle, &ctxt))
return -1;
- if (desc->magic != XENCOMM_MAGIC) {
- printk("%s error: %p magic was 0x%x\n", __func__, desc,
desc->magic);
- return -1;
- }
-
/* iterate through the descriptor incrementing addresses */
- while ((bytes > 0) && (i < desc->nr_addrs)) {
- unsigned long dest_paddr = desc->address[i];
+ while ((bytes > 0) && (i < xencomm_ctxt_nr_addrs(&ctxt)))
{
+ unsigned long *address = xencomm_ctxt_address(&ctxt, i);
+ unsigned long dest_paddr = *address;
unsigned int pgoffset;
unsigned int chunksz;
unsigned int chunk_skip;
@@ -303,34 +427,38 @@ int xencomm_add_offset(void **handle, un
chunk_skip = min(chunksz, bytes);
if (chunk_skip == chunksz) {
/* exhausted this page */
- desc->address[i] = XENCOMM_INVALID;
+ *address = XENCOMM_INVALID;
} else {
- desc->address[i] += chunk_skip;
+ *address += chunk_skip;
}
bytes -= chunk_skip;
i++;
}
+ xencomm_ctxt_done(&ctxt);
return 0;
}
int xencomm_handle_is_null(void *handle)
{
- struct xencomm_desc *desc;
+ struct xencomm_ctxt ctxt;
int i;
+ int res = 1;
if (xencomm_is_inline(handle))
return xencomm_inline_addr(handle) == 0;
- desc = (struct xencomm_desc *)
- xencomm_maddr_to_vaddr(paddr_to_maddr((unsigned long)handle));
- if (desc == NULL)
+ if (xencomm_ctxt_init(handle, &ctxt))
return 1;
- for (i = 0; i < desc->nr_addrs; i++)
- if (desc->address[i] != XENCOMM_INVALID)
- return 0;
-
- return 1;
-}
-
+ for (i = 0; i < xencomm_ctxt_nr_addrs(&ctxt); i++) {
+ if (*xencomm_ctxt_address(&ctxt, i) != XENCOMM_INVALID) {
+ res = 0;
+ goto out;
+ }
+ }
+
+out:
+ xencomm_ctxt_done(&ctxt);
+ return res;
+}
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