[PATCH 5.1 25/55] efi/memreserve: deal with memreserve entries in unmapped memory

From: Greg Kroah-Hartman
Date: Tue Jul 02 2019 - 04:03:48 EST


From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

commit 18df7577adae6c6c778bf774b3aebcacbc1fb439 upstream.

Ensure that the EFI memreserve entries can be accessed, even if they
are located in memory that the kernel (e.g., a crashkernel) omits from
the linear map.

Fixes: 80424b02d42b ("efi: Reduce the amount of memblock reservations ...")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.0+
Reported-by: Jonathan Richardson <jonathan.richardson@xxxxxxxxxxxx>
Reviewed-by: Jonathan Richardson <jonathan.richardson@xxxxxxxxxxxx>
Tested-by: Jonathan Richardson <jonathan.richardson@xxxxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/firmware/efi/efi.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -1007,14 +1007,16 @@ int __ref efi_mem_reserve_persistent(phy

/* first try to find a slot in an existing linked list entry */
for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
- rsv = __va(prsv);
+ rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
if (index < rsv->size) {
rsv->entry[index].base = addr;
rsv->entry[index].size = size;

+ memunmap(rsv);
return 0;
}
+ memunmap(rsv);
}

/* no slot found - allocate a new linked list entry */
@@ -1022,7 +1024,13 @@ int __ref efi_mem_reserve_persistent(phy
if (!rsv)
return -ENOMEM;

- rsv->size = EFI_MEMRESERVE_COUNT(PAGE_SIZE);
+ /*
+ * The memremap() call above assumes that a linux_efi_memreserve entry
+ * never crosses a page boundary, so let's ensure that this remains true
+ * even when kexec'ing a 4k pages kernel from a >4k pages kernel, by
+ * using SZ_4K explicitly in the size calculation below.
+ */
+ rsv->size = EFI_MEMRESERVE_COUNT(SZ_4K);
atomic_set(&rsv->count, 1);
rsv->entry[0].base = addr;
rsv->entry[0].size = size;