[PATCH v2 4/6] efi: memmap: Disregard bogus entries instead of returning them

[Ard Biesheuvel <ardb@xxxxxxxxxx>]

The ESRT code currently contains some sanity checks on the memory
descriptor it obtains, but these can only trigger when the descriptor is
invalid (if at all).

So let's drop these checks, and instead, disregard descriptors entirely
if the start address is misaligned, or the number of pages reaches
beyond the end of the address space. Note that the memory map as a whole
could still be inconsistent, i.e., multiple entries might cover the same
area, or the address could be outside of the addressable VA space, but
validating that goes beyond the scope of these helpers.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
 drivers/firmware/efi/efi.c  | 13 +++++++------
 drivers/firmware/efi/esrt.c | 18 +-----------------
 2 files changed, 8 insertions(+), 23 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 11857af72859..55bd3f4aab28 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -461,19 +461,20 @@ int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t 
*out_md)
        efi_memory_desc_t *md;
 
        if (!efi_enabled(EFI_MEMMAP)) {
-               pr_err_once("EFI_MEMMAP is not enabled.\n");
+               pr_warn_once("EFI_MEMMAP is not enabled.\n");
                return -EINVAL;
        }
 
-       if (!out_md) {
-               pr_err_once("out_md is null.\n");
-               return -EINVAL;
-        }
-
        for_each_efi_memory_desc(md) {
                u64 size;
                u64 end;
 
+               /* skip bogus entries */
+               if ((md->phys_addr & (EFI_PAGE_SIZE - 1)) ||
+                   (md->phys_addr > 0 &&
+                    (md->num_pages > (U64_MAX - md->phys_addr + 1) >> 
EFI_PAGE_SHIFT)))
+                       continue;
+
                size = md->num_pages << EFI_PAGE_SHIFT;
                end = md->phys_addr + size;
                if (phys_addr >= md->phys_addr && phys_addr < end) {
diff --git a/drivers/firmware/efi/esrt.c b/drivers/firmware/efi/esrt.c
index 2a2f52b017e7..8f86f2b0734b 100644
--- a/drivers/firmware/efi/esrt.c
+++ b/drivers/firmware/efi/esrt.c
@@ -247,9 +247,6 @@ void __init efi_esrt_init(void)
        int rc;
        phys_addr_t end;
 
-       if (!efi_enabled(EFI_MEMMAP))
-               return;
-
        pr_debug("esrt-init: loading.\n");
        if (!esrt_table_exists())
                return;
@@ -263,21 +260,8 @@ void __init efi_esrt_init(void)
                return;
        }
 
-       max = efi_mem_desc_end(&md);
-       if (max < efi.esrt) {
-               pr_err("EFI memory descriptor is invalid. (esrt: %p max: %p)\n",
-                      (void *)efi.esrt, (void *)max);
-               return;
-       }
-
+       max = efi_mem_desc_end(&md) - efi.esrt;
        size = sizeof(*esrt);
-       max -= efi.esrt;
-
-       if (max < size) {
-               pr_err("ESRT header doesn't fit on single memory map entry. 
(size: %zu max: %zu)\n",
-                      size, max);
-               return;
-       }
 
        va = early_memremap(efi.esrt, size);
        if (!va) {
-- 
2.35.1