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[Xen-devel] [PATCH 3/7] xencomm take 3: xen side fix invalid or racy acc

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH 3/7] xencomm take 3: xen side fix invalid or racy access
From: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
Date: Tue, 14 Aug 2007 18:50:23 +0900
Cc: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx, xen-ppc-devel@xxxxxxxxxxxxxxxxxxx
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# HG changeset patch
# User yamahata@xxxxxxxxxxxxx
# 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@xxxxxxxxxxxxx>

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;
+}

Attachment: 15727_cf7a9141e7f8_fix_xencomm_invalid_racy_access.patch
Description: Text Data

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