linux-kernel - [PATCH] arm64: kaslr: Use standard early random function

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Message-Id: <20200807004904.72893-1-linux@roeck-us.net>
Date:   Thu,  6 Aug 2020 17:49:04 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Daniel Díaz <daniel.diaz@...aro.org>,
        tytso@....edu, Guenter Roeck <linux@...ck-us.net>,
        Qian Cai <cai@....pw>, Mark Brown <broonie@...nel.org>
Subject: [PATCH] arm64: kaslr: Use standard early random function

Commit 585524081ecd ("random: random.h should include archrandom.h, not
the other way around") tries to fix a problem with recursive inclusion
of linux/random.h and arch/archrandom.h for arm64. Unfortunately, this
results in the following compile error if ARCH_RANDOM is disabled.

arch/arm64/kernel/kaslr.c: In function 'kaslr_early_init':
arch/arm64/kernel/kaslr.c:128:6: error: implicit declaration of function
'__early_cpu_has_rndr'; did you mean '__early_pfn_to_nid'?
[-Werror=implicit-function-declaration]
  if (__early_cpu_has_rndr()) {
      ^~~~~~~~~~~~~~~~~~~~
      __early_pfn_to_nid
arch/arm64/kernel/kaslr.c:131:7: error: implicit declaration of function
'__arm64_rndr' [-Werror=implicit-function-declaration]
   if (__arm64_rndr(&raw))
       ^~~~~~~~~~~~

Problem is that arch/archrandom.h is only included from linux/random.h if
ARCH_RANDOM is enabled. If not, __arm64_rndr() and __early_cpu_has_rndr()
are undeclared, causing the problem.

Use arch_get_random_seed_long_early() instead of arm64 specific functions
to solve the problem. As a side effect of this change, the code no longer
bypasses ARCH_RANDOM, which I consider desirable (after all, ARCH_RANDOM
was disabled for a reason).

Reported-by: Qian Cai <cai@....pw>
Fixes: 585524081ecd ("random: random.h should include archrandom.h, not the other way around")
Fixes: 2e8e1ea88cbc ("arm64: Use v8.5-RNG entropy for KASLR seed")
Cc: Qian Cai <cai@....pw>
Cc: Mark Brown <broonie@...nel.org>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 arch/arm64/kernel/kaslr.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 9ded4237e1c1..b181e0544b79 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -84,6 +84,7 @@ u64 __init kaslr_early_init(u64 dt_phys)
 	void *fdt;
 	u64 seed, offset, mask, module_range;
 	const u8 *cmdline, *str;
+	unsigned long raw;
 	int size;
 
 	/*
@@ -122,15 +123,12 @@ u64 __init kaslr_early_init(u64 dt_phys)
 	}
 
 	/*
-	 * Mix in any entropy obtainable architecturally, open coded
-	 * since this runs extremely early.
+	 * Mix in any entropy obtainable architecturally if enabled
+	 * and supported.
 	 */
-	if (__early_cpu_has_rndr()) {
-		unsigned long raw;
 
-		if (__arm64_rndr(&raw))
-			seed ^= raw;
-	}
+	if (arch_get_random_seed_long_early(&raw))
+		seed ^= raw;
 
 	if (!seed) {
 		kaslr_status = KASLR_DISABLED_NO_SEED;
-- 
2.17.1