[PATCH v2] x86: selective remapping in parse_setup_data()

[Linn Crosetto <linn@hp.com>]

Type SETUP_PCI, added by setup_efi_pci(), may advertise a ROM size
larger than early_memremap() is able to handle, which is currently
limited to 256kB. If this occurs it leads to a NULL dereference in
parse_setup_data().

To avoid this, first remap the setup_data header, and remap the data
only for types actually parsed in parse_setup_data(). Type SETUP_PCI is
handled later by pcibios_add_device(), when ioremap() is available.

Signed-off-by: Linn Crosetto <linn@hp.com>
---
v2: add more detail to the explanation as requested by hpa
---
 arch/x86/kernel/setup.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f8ec578..2063a49 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -423,6 +423,17 @@ static void __init reserve_initrd(void)
 }
 #endif /* CONFIG_BLK_DEV_INITRD */
 
+static void __init remap_setup_data(u64 pa_data, u32 data_len,
+				    struct setup_data **data, u32 *map_len)
+{
+	if (data_len <= *map_len)
+		return;
+
+	early_iounmap(*data, *map_len);
+	*data = early_memremap(pa_data, data_len);
+	*map_len = data_len;
+}
+
 static void __init parse_setup_data(void)
 {
 	struct setup_data *data;
@@ -432,18 +443,16 @@ static void __init parse_setup_data(void)
 	while (pa_data) {
 		u32 data_len, map_len;
 
+		/* The data length may be too large for early remapping,
+		   remap the data only when needed. */
 		map_len = max(PAGE_SIZE - (pa_data & ~PAGE_MASK),
 			      (u64)sizeof(struct setup_data));
 		data = early_memremap(pa_data, map_len);
 		data_len = data->len + sizeof(struct setup_data);
-		if (data_len > map_len) {
-			early_iounmap(data, map_len);
-			data = early_memremap(pa_data, data_len);
-			map_len = data_len;
-		}
 
 		switch (data->type) {
 		case SETUP_E820_EXT:
+			remap_setup_data(pa_data, data_len, &data, &map_len);
 			parse_e820_ext(data);
 			break;
 		case SETUP_DTB:
-- 
1.7.11.3