[PATCH V2 1/2] efi/unaccepted: Do not let /proc/vmcore try to access unaccepted memory

From: Adrian Hunter <adrian.hunter@intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ard Biesheuvel <ardb@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Lorenzo Stoakes <lstoakes@gmail.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Baoquan He <bhe@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-coco@lists.linux.dev,
	linux-efi@vger.kernel.org, kexec@lists.infradead.org
Subject: [PATCH V2 1/2] efi/unaccepted: Do not let /proc/vmcore try to access unaccepted memory
Date: Mon, 11 Sep 2023 14:21:13 +0300	[thread overview]
Message-ID: <20230911112114.91323-2-adrian.hunter@intel.com> (raw)
In-Reply-To: <20230911112114.91323-1-adrian.hunter@intel.com>

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 let /proc/vmcore try to access unaccepted memory because it can
cause the guest to fail.

For /proc/vmcore, which is read-only, this means a read or mmap of
unaccepted memory will return zeros.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 drivers/firmware/efi/unaccepted_memory.c | 20 ++++++++++++++++++++
 include/linux/mm.h                       |  7 +++++++
 2 files changed, 27 insertions(+)


Changes in V2:

          Change patch subject and commit message
          Use vmcore_cb->.pfn_is_ram() instead of changing vmcore.c

diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index 853f7dc3c21d..79ba576b22e3 100644
--- a/drivers/firmware/efi/unaccepted_memory.c
+++ b/drivers/firmware/efi/unaccepted_memory.c
@@ -3,6 +3,7 @@
 #include <linux/efi.h>
 #include <linux/memblock.h>
 #include <linux/spinlock.h>
+#include <linux/crash_dump.h>
 #include <asm/unaccepted_memory.h>
 
 /* Protects unaccepted memory bitmap */
@@ -145,3 +146,22 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
 
 	return ret;
 }
+
+#ifdef CONFIG_PROC_VMCORE
+static bool unaccepted_memory_vmcore_pfn_is_ram(struct vmcore_cb *cb,
+						unsigned long pfn)
+{
+	return !pfn_is_unaccepted_memory(pfn);
+}
+
+static struct vmcore_cb vmcore_cb = {
+	.pfn_is_ram = unaccepted_memory_vmcore_pfn_is_ram,
+};
+
+static int __init unaccepted_memory_init_kdump(void)
+{
+	register_vmcore_cb(&vmcore_cb);
+	return 0;
+}
+core_initcall(unaccepted_memory_init_kdump);
+#endif /* CONFIG_PROC_VMCORE */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bf5d0b1b16f4..86511150f1d4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4062,4 +4062,11 @@ static inline void accept_memory(phys_addr_t start, phys_addr_t end)
 
 #endif
 
+static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
+{
+	phys_addr_t paddr = pfn << PAGE_SHIFT;
+
+	return range_contains_unaccepted_memory(paddr, paddr + PAGE_SIZE);
+}
+
 #endif /* _LINUX_MM_H */
-- 
2.34.1

