Re: [PATCH] arm64: kaslr: don't pretend KASLR is enabled if offset < MIN_KIMG_ALIGN

---
I have sent out the same patch with a much shorter commit log as part of
my LPA2 series before, but I only realized today that this is likely to
fix most occurrences of the issue where a single 10g vmalloc() call
break subsequent module loading, so I am reposting it in isolation.

 arch/arm64/include/asm/memory.h | 11 +++++++++++
 arch/arm64/kernel/cpufeature.c  |  2 +-
 arch/arm64/kernel/kaslr.c       |  2 +-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 9dd08cd339c3f028..78e5163836a0ab95 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h

@@ -180,6 +180,7 @@
 #include <linux/compiler.h>
 #include <linux/mmdebug.h>
 #include <linux/types.h>
+#include <asm/boot.h>
 #include <asm/bug.h>
 
 #if VA_BITS > 48

@@ -203,6 +204,16 @@ static inline unsigned long kaslr_offset(void)
 	return kimage_vaddr - KIMAGE_VADDR;
 }
 
+static inline bool kaslr_enabled(void)
+{
+	/*
+	 * The KASLR offset modulo MIN_KIMG_ALIGN is taken from the physical
+	 * placement of the image rather than from the seed, so a displacement
+	 * of less than MIN_KIMG_ALIGN means that no seed was provided.
+	 */
+	return kaslr_offset() >= MIN_KIMG_ALIGN;
+}
+
 /*
  * Allow all memory at the discovery stage. We will clip it later.
  */

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 45a42cf2191c36c3..5643a9ca502af207 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -1633,7 +1633,7 @@ bool kaslr_requires_kpti(void)
 			return false;
 	}
 
-	return kaslr_offset() > 0;
+	return kaslr_enabled();
 }
 
 static bool __meltdown_safe = true;

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 325455d16dbcb31a..e7477f21a4c9d062 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c

@@ -41,7 +41,7 @@ static int __init kaslr_init(void)
 		return 0;
 	}
 
-	if (!kaslr_offset()) {
+	if (!kaslr_enabled()) {
 		pr_warn("KASLR disabled due to lack of seed\n");
 		return 0;
 	}

-- 
2.39.1