[v2] arm64: kaslr: warning linear region randomization on failure

Commit Message

Keun-O Park March 4, 2025, 4:26 a.m. UTC

From: Keuno Park <[e-mail]>

On systems using 4KB pages and having 39 VA_BITS, linear_region_size
gets 256GiB space. It was observed that some SoCs such as Qualcomm
QCM8550 returns 40bits of PA range from MMFR0_EL1. This leads range
value to have minus as the variable range is s64, so that all the
calculations for randomizing linear address space are skipped.
As a result of this, the kernel's linear region is not randomized.
For hotplug memory users, kernel needs to inform that linear region
is not randomized. However, if CONFIG_MEMORY_HOTPLUG is turned off,
then kernel tries to fall back to the legacy way to randomize linear
region.

Change-Id: Ib29e45f44928937881d514fb87b4cac828b5a3f5
Fixes: 97d6786e0669 ("arm64: mm: account for hotplug memory when randomizing the linear region")
Signed-off-by: Keuno Park <[e-mail]>
---
 arch/arm64/mm/init.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Patch

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9c0b8d9558fc..848790a9e75e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -290,6 +290,17 @@  void __init arm64_memblock_init(void)
 		s64 range = linear_region_size -
 			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
 
+		if (range < 0) {
+			if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
+				WARN(true, "linear region is not randomized due to bigger parange\n");
+			} else {
+				pr_warn("falling back to the range considering on-boot DRAM size\n");
+				range = linear_region_size -
+					(memblock_end_of_DRAM() -
+					 memblock_start_of_DRAM());
+			}
+		}
+
 		/*
 		 * If the size of the linear region exceeds, by a sufficient
 		 * margin, the size of the region that the physical memory can