Patch "of/fdt: Make sure no-map does not remove already reserved regions" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    of/fdt: Make sure no-map does not remove already reserved regions

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     of-fdt-make-sure-no-map-does-not-remove-already-rese.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0f184af1a2c6c85cb479f7e96d114a98615b33d1
Author: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
Date:   Fri Jan 15 11:45:44 2021 +0000

    of/fdt: Make sure no-map does not remove already reserved regions
    
    [ Upstream commit 8a5a75e5e9e55de1cef5d83ca3589cb4899193ef ]
    
    If the device tree is incorrectly configured, and attempts to
    define a "no-map" reserved memory that overlaps with the kernel
    data/code, the kernel would crash quickly after boot, with no
    obvious clue about the nature of the issue.
    
    For example, this would happen if we have the kernel mapped at
    these addresses (from /proc/iomem):
    40000000-41ffffff : System RAM
      40080000-40dfffff : Kernel code
      40e00000-411fffff : reserved
      41200000-413e0fff : Kernel data
    
    And we declare a no-map shared-dma-pool region at a fixed address
    within that range:
    mem_reserved: mem_region {
            compatible = "shared-dma-pool";
            reg = <0 0x40000000 0 0x01A00000>;
            no-map;
    };
    
    To fix this, when removing memory regions at early boot (which is
    what "no-map" regions do), we need to make sure that the memory
    is not already reserved. If we do, __reserved_mem_reserve_reg
    will throw an error:
    [    0.000000] OF: fdt: Reserved memory: failed to reserve memory
       for node 'mem_region': base 0x0000000040000000, size 26 MiB
    and the code that will try to use the region should also fail,
    later on.
    
    We do not do anything for non-"no-map" regions, as memblock
    explicitly allows reserved regions to overlap, and the commit
    that this fixes removed the check for that precise reason.
    
    [ qperret: fixed conflicts caused by the usage of memblock_mark_nomap ]
    
    Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
    Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
    Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
    Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20210115114544.1830068-3-qperret@xxxxxxxxxx
    Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 036af904e0cfa..fc24102e25ce7 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -1153,8 +1153,16 @@ int __init __weak early_init_dt_mark_hotplug_memory_arch(u64 base, u64 size)
 int __init __weak early_init_dt_reserve_memory_arch(phys_addr_t base,
 					phys_addr_t size, bool nomap)
 {
-	if (nomap)
+	if (nomap) {
+		/*
+		 * If the memory is already reserved (by another region), we
+		 * should not allow it to be marked nomap.
+		 */
+		if (memblock_is_region_reserved(base, size))
+			return -EBUSY;
+
 		return memblock_mark_nomap(base, size);
+	}
 	return memblock_reserve(base, size);
 }