From d7c19014762ae0a2f46d61a8385c3c84dde09bea Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Sat, 1 Feb 2025 18:21:35 +0100
Subject: [PATCH] efi: Avoid cold plugged memory for placing the kernel
commit ba69e0750b0362870294adab09339a0c39c3beaf upstream.
UEFI 2.11 introduced EFI_MEMORY_HOT_PLUGGABLE to annotate system memory
regions that are 'cold plugged' at boot, i.e., hot pluggable memory that
is available from early boot, and described as system RAM by the
firmware.
Existing loaders and EFI applications running in the boot context will
happily use this memory for allocating data structures that cannot be
freed or moved at runtime, and this prevents the memory from being
unplugged. Going forward, the new EFI_MEMORY_HOT_PLUGGABLE attribute
should be tested, and memory annotated as such should be avoided for
such allocations.
In the EFI stub, there are a couple of occurrences where, instead of the
high-level AllocatePages() UEFI boot service, a low-level code sequence
is used that traverses the EFI memory map and carves out the requested
number of pages from a free region. This is needed, e.g., for allocating
as low as possible, or for allocating pages at random.
While AllocatePages() should presumably avoid special purpose memory and
cold plugged regions, this manual approach needs to incorporate this
logic itself, in order to prevent the kernel itself from ending up in a
hot unpluggable region, preventing it from being unplugged.
So add the EFI_MEMORY_HOTPLUGGABLE macro definition, and check for it
where appropriate.
Cc: stable@vger.kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/firmware/efi/efi.c | 6 ++++--
drivers/firmware/efi/libstub/randomalloc.c | 3 +++
drivers/firmware/efi/libstub/relocate.c | 3 +++
include/linux/efi.h | 1 +
4 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 28d4defc5d0cd..9786dfff9f840 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -835,13 +835,15 @@ char * __init efi_md_typeattr_format(char *buf, size_t size,
EFI_MEMORY_WB | EFI_MEMORY_UCE | EFI_MEMORY_RO |
EFI_MEMORY_WP | EFI_MEMORY_RP | EFI_MEMORY_XP |
EFI_MEMORY_NV | EFI_MEMORY_SP | EFI_MEMORY_CPU_CRYPTO |
- EFI_MEMORY_RUNTIME | EFI_MEMORY_MORE_RELIABLE))
+ EFI_MEMORY_MORE_RELIABLE | EFI_MEMORY_HOT_PLUGGABLE |
+ EFI_MEMORY_RUNTIME))
snprintf(pos, size, "|attr=0x%016llx]",
(unsigned long long)attr);
else
snprintf(pos, size,
- "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",
+ "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",
attr & EFI_MEMORY_RUNTIME ? "RUN" : "",
+ attr & EFI_MEMORY_HOT_PLUGGABLE ? "HP" : "",
attr & EFI_MEMORY_MORE_RELIABLE ? "MR" : "",
attr & EFI_MEMORY_CPU_CRYPTO ? "CC" : "",
attr & EFI_MEMORY_SP ? "SP" : "",
diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c
index fff826f56728c..5d88a5a46b094 100644
--- a/drivers/firmware/efi/libstub/randomalloc.c
+++ b/drivers/firmware/efi/libstub/randomalloc.c
@@ -25,6 +25,9 @@ static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
if (md->type != EFI_CONVENTIONAL_MEMORY)
return 0;
+ if (md->attribute & EFI_MEMORY_HOT_PLUGGABLE)
+ return 0;
+
if (efi_soft_reserve_enabled() &&
(md->attribute & EFI_MEMORY_SP))
return 0;
diff --git a/drivers/firmware/efi/libstub/relocate.c b/drivers/firmware/efi/libstub/relocate.c
index bf6fbd5d22a1a..713ee2de02cf3 100644
--- a/drivers/firmware/efi/libstub/relocate.c
+++ b/drivers/firmware/efi/libstub/relocate.c
@@ -53,6 +53,9 @@ efi_status_t efi_low_alloc_above(unsigned long size, unsigned long align,
if (desc->type != EFI_CONVENTIONAL_MEMORY)
continue;
+ if (desc->attribute & EFI_MEMORY_HOT_PLUGGABLE)
+ continue;
+
if (efi_soft_reserve_enabled() &&
(desc->attribute & EFI_MEMORY_SP))
continue;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a849b533be5b1..1d73c77051c09 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -125,6 +125,7 @@ typedef struct {
#define EFI_MEMORY_RO ((u64)0x0000000000020000ULL) /* read-only */
#define EFI_MEMORY_SP ((u64)0x0000000000040000ULL) /* soft reserved */
#define EFI_MEMORY_CPU_CRYPTO ((u64)0x0000000000080000ULL) /* supports encryption */
+#define EFI_MEMORY_HOT_PLUGGABLE BIT_ULL(20) /* supports unplugging at runtime */
#define EFI_MEMORY_RUNTIME ((u64)0x8000000000000000ULL) /* range requires runtime mapping */
#define EFI_MEMORY_DESCRIPTOR_VERSION 1
--
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