iscsi_ibft: fix crash due to KASLR physical memory remapping

Starting with commit a799c2b
("x86/setup: Consolidate early memory reservations")
memory reservations have been moved earlier during the boot process,
before the execution of the Kernel Address Space Layout Randomization code.

setup_arch() calls the iscsi_ibft's find_ibft_region() function
to find and reserve the memory dedicated to the iBFT and this function
also saves a virtual pointer to the iBFT table for later use.

The problem is that if KALSR is active, the physical memory gets
remapped somewhere else in the virtual address space and the pointer is
no longer valid, this will cause a kernel panic when the iscsi driver tries
to dereference it.

 iBFT detected.
 BUG: unable to handle page fault for address: ffff888000099fd8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] SMP PTI

..snip..

 Call Trace:
  ? ibft_create_kobject+0x1d2/0x1d2 [iscsi_ibft]
  do_one_initcall+0x44/0x1d0
  ? kmem_cache_alloc_trace+0x119/0x220
  do_init_module+0x5c/0x270
  __do_sys_init_module+0x12e/0x1b0
  do_syscall_64+0x40/0x80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix this bug by saving the address of the physical location
of the ibft; later the driver will use isa_bus_to_virt() to get
the correct virtual address.

N.B. On each reboot KASLR randomizes the virtual addresses so
assuming phys_to_virt before KASLR does its deed is incorrect.

Simplify the code by renaming find_ibft_region()
to reserve_ibft_region() and remove all the wrappers.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>

arch/x86/kernel/setup.c

@@ -571,16 +571,6 @@ void __init reserve_standard_io_resources(void)
 
 }
 
-static __init void reserve_ibft_region(void)
-{
-	unsigned long addr, size = 0;
-
-	addr = find_ibft_region(&size);
-
-	if (size)
-		memblock_reserve(addr, size);
-}
-
 static bool __init snb_gfx_workaround_needed(void)
 {
 #ifdef CONFIG_PCI

drivers/firmware/iscsi_ibft.c

@@ -84,8 +84,10 @@ MODULE_DESCRIPTION("sysfs interface to BIOS iBFT information");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(IBFT_ISCSI_VERSION);
 
+static struct acpi_table_ibft *ibft_addr;
+
 #ifndef CONFIG_ISCSI_IBFT_FIND
-struct acpi_table_ibft *ibft_addr;
+phys_addr_t ibft_phys_addr;
 #endif
 
 struct ibft_hdr {
@@ -858,11 +860,13 @@ static int __init ibft_init(void)
 	int rc = 0;
 
 	/*
-	   As on UEFI systems the setup_arch()/find_ibft_region()
+	   As on UEFI systems the setup_arch()/reserve_ibft_region()
 	   is called before ACPI tables are parsed and it only does
 	   legacy finding.
 	*/
-	if (!ibft_addr)
+	if (ibft_phys_addr)
+		ibft_addr = isa_bus_to_virt(ibft_phys_addr);
+	else
 		acpi_find_ibft_region();
 
 	if (ibft_addr) {

drivers/firmware/iscsi_ibft_find.c

@@ -31,8 +31,8 @@
 /*
  * Physical location of iSCSI Boot Format Table.
  */
-struct acpi_table_ibft *ibft_addr;
-EXPORT_SYMBOL_GPL(ibft_addr);
+phys_addr_t ibft_phys_addr;
+EXPORT_SYMBOL_GPL(ibft_phys_addr);
 
 static const struct {
 	char *sign;
@@ -47,13 +47,24 @@ static const struct {
 #define VGA_MEM 0xA0000 /* VGA buffer */
 #define VGA_SIZE 0x20000 /* 128kB */
 
-static int __init find_ibft_in_mem(void)
+/*
+ * Routine used to find and reserve the iSCSI Boot Format Table
+ */
+void __init reserve_ibft_region(void)
 {
 	unsigned long pos;
 	unsigned int len = 0;
 	void *virt;
 	int i;
 
+	ibft_phys_addr = 0;
+
+	/* iBFT 1.03 section 1.4.3.1 mandates that UEFI machines will
+	 * only use ACPI for this
+	 */
+	if (efi_enabled(EFI_BOOT))
+		return;
+
 	for (pos = IBFT_START; pos < IBFT_END; pos += 16) {
 		/* The table can't be inside the VGA BIOS reserved space,
 		 * so skip that area */
@@ -70,35 +81,12 @@ static int __init find_ibft_in_mem(void)
 				/* if the length of the table extends past 1M,
 				 * the table cannot be valid. */
 				if (pos + len <= (IBFT_END-1)) {
-					ibft_addr = (struct acpi_table_ibft *)virt;
-					pr_info("iBFT found at 0x%lx.\n", pos);
-					goto done;
+					ibft_phys_addr = pos;
+					memblock_reserve(ibft_phys_addr, PAGE_ALIGN(len));
+					pr_info("iBFT found at 0x%lx.\n", ibft_phys_addr);
+					return;
 				}
 			}
 		}
 	}
-done:
-	return len;
-}
-/*
- * Routine used to find the iSCSI Boot Format Table. The logical
- * kernel address is set in the ibft_addr global variable.
- */
-unsigned long __init find_ibft_region(unsigned long *sizep)
-{
-	ibft_addr = NULL;
-
-	/* iBFT 1.03 section 1.4.3.1 mandates that UEFI machines will
-	 * only use ACPI for this */
-
-	if (!efi_enabled(EFI_BOOT))
-		find_ibft_in_mem();
-
-	if (ibft_addr) {
-		*sizep = PAGE_ALIGN(ibft_addr->header.length);
-		return (u64)virt_to_phys(ibft_addr);
-	}
-
-	*sizep = 0;
-	return 0;
 }

include/linux/iscsi_ibft.h

@@ -13,26 +13,22 @@
 #ifndef ISCSI_IBFT_H
 #define ISCSI_IBFT_H
 
-#include <linux/acpi.h>
+#include <linux/types.h>
 
 /*
- * Logical location of iSCSI Boot Format Table.
- * If the value is NULL there is no iBFT on the machine.
+ * Physical location of iSCSI Boot Format Table.
+ * If the value is 0 there is no iBFT on the machine.
  */
-extern struct acpi_table_ibft *ibft_addr;
+extern phys_addr_t ibft_phys_addr;
 
 /*
  * Routine used to find and reserve the iSCSI Boot Format Table. The
- * mapped address is set in the ibft_addr variable.
+ * physical address is set in the ibft_phys_addr variable.
  */
 #ifdef CONFIG_ISCSI_IBFT_FIND
-unsigned long find_ibft_region(unsigned long *sizep);
+void reserve_ibft_region(void);
 #else
-static inline unsigned long find_ibft_region(unsigned long *sizep)
-{
-	*sizep = 0;
-	return 0;
-}
+static inline void reserve_ibft_region(void) {}
 #endif
 
 #endif /* ISCSI_IBFT_H */