linux-kernel - [PATCH 3/3] /dev/mem: Do not map unaccepted memory

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Date:   Wed,  6 Sep 2023 10:39:02 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-coco@...ts.linux.dev, linux-efi@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: [PATCH 3/3] /dev/mem: Do not map unaccepted memory

Support for unaccepted memory was added recently, refer commit
dcdfdd40fa82 ("mm: Add support for unaccepted memory"), whereby
a virtual machine may need to accept memory before it can be used.

Do not map unaccepted memory because it can cause the guest to fail.

For /dev/mem, this means a read of unaccepted memory will return zeros,
a write to unaccepted memory will be ignored, but an mmap of unaccepted
memory will return an error.

Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 drivers/char/mem.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 1052b0f2d4cf..1a7c5728783c 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -147,7 +147,8 @@ static ssize_t read_mem(struct file *file, char __user *buf,
 			goto failed;
 
 		err = -EFAULT;
-		if (allowed == 2) {
+		if (allowed == 2 ||
+		    range_contains_unaccepted_memory(p, p + sz)) {
 			/* Show zeros for restricted memory. */
 			remaining = clear_user(buf, sz);
 		} else {
@@ -226,7 +227,8 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 			return -EPERM;
 
 		/* Skip actual writing when a page is marked as restricted. */
-		if (allowed == 1) {
+		if (allowed == 1 &&
+		    !range_contains_unaccepted_memory(p, p + sz)) {
 			/*
 			 * On ia64 if a page has been mapped somewhere as
 			 * uncached, then it must also be accessed uncached
@@ -378,6 +380,9 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 						&vma->vm_page_prot))
 		return -EINVAL;
 
+	if (range_contains_unaccepted_memory(offset, offset + size))
+		return -EINVAL;
+
 	vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
 						 size,
 						 vma->vm_page_prot);
-- 
2.34.1