efi/unaccepted: do not let /proc/vmcore try to access unaccepted memory

Patch series "Do not try to access unaccepted memory", v2.

Support for unaccepted memory was added recently, refer commit
dcdfdd40 ("mm: Add support for unaccepted memory"), whereby
a virtual machine may need to accept memory before it can be used.

Plug a few gaps where RAM is exposed without checking if it is
unaccepted memory.


This patch (of 2):

Support for unaccepted memory was added recently, refer commit
dcdfdd40 ("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.

Link: https://lkml.kernel.org/r/20230911112114.91323-1-adrian.hunter@intel.com
Link: https://lkml.kernel.org/r/20230911112114.91323-2-adrian.hunter@intel.comSigned-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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 */

include/linux/mm.h

@@ -4054,4 +4054,11 @@ 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 */