[PATCH v6 28/41] arm64: kaslr: Use feature override instead of parsing the cmdline again

From: Ard Biesheuvel <ardb@google.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	 Ryan Roberts <ryan.roberts@arm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	 Kees Cook <keescook@chromium.org>
Subject: [PATCH v6 28/41] arm64: kaslr: Use feature override instead of parsing the cmdline again
Date: Wed, 29 Nov 2023 12:16:24 +0100	[thread overview]
Message-ID: <20231129111555.3594833-71-ardb@google.com> (raw)
In-Reply-To: <20231129111555.3594833-43-ardb@google.com>

From: Ard Biesheuvel <ardb@kernel.org>

The early kaslr code open codes the detection of 'nokaslr' on the kernel
command line, and this is no longer necessary now that the feature
detection code, which also looks for the same string, executes before
this code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h |  5 ++
 arch/arm64/kernel/kaslr.c           |  4 +-
 arch/arm64/kernel/pi/kaslr_early.c  | 53 +-------------------
 3 files changed, 7 insertions(+), 55 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a41cb0bc220b..9e8c3e345951 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -948,6 +948,11 @@ static inline bool arm64_test_sw_feature_override(int feat)
 					    &arm64_sw_feature_override);
 }
 
+static inline bool kaslr_disabled_cmdline(void)
+{
+	return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOKASLR);
+}
+
 u32 get_kvm_ipa_limit(void);
 void dump_cpu_features(void);
 
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 12c7f3c8ba76..1da3e25f9d9e 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -16,9 +16,7 @@ bool __ro_after_init __kaslr_is_enabled = false;
 
 void __init kaslr_init(void)
 {
-	if (cpuid_feature_extract_unsigned_field(arm64_sw_feature_override.val &
-						 arm64_sw_feature_override.mask,
-						 ARM64_SW_FEATURE_OVERRIDE_NOKASLR)) {
+	if (kaslr_disabled_cmdline()) {
 		pr_info("KASLR disabled on command line\n");
 		return;
 	}
diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
index 167081b30a15..f2305e276ec3 100644
--- a/arch/arm64/kernel/pi/kaslr_early.c
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -16,57 +16,6 @@
 #include <asm/memory.h>
 #include <asm/pgtable.h>
 
-/* taken from lib/string.c */
-static char *__init __strstr(const char *s1, const char *s2)
-{
-	size_t l1, l2;
-
-	l2 = strlen(s2);
-	if (!l2)
-		return (char *)s1;
-	l1 = strlen(s1);
-	while (l1 >= l2) {
-		l1--;
-		if (!memcmp(s1, s2, l2))
-			return (char *)s1;
-		s1++;
-	}
-	return NULL;
-}
-static bool __init cmdline_contains_nokaslr(const u8 *cmdline)
-{
-	const u8 *str;
-
-	str = __strstr(cmdline, "nokaslr");
-	return str == cmdline || (str > cmdline && *(str - 1) == ' ');
-}
-
-static bool __init is_kaslr_disabled_cmdline(void *fdt)
-{
-	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
-		int node;
-		const u8 *prop;
-
-		node = fdt_path_offset(fdt, "/chosen");
-		if (node < 0)
-			goto out;
-
-		prop = fdt_getprop(fdt, node, "bootargs", NULL);
-		if (!prop)
-			goto out;
-
-		if (cmdline_contains_nokaslr(prop))
-			return true;
-
-		if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
-			goto out;
-
-		return false;
-	}
-out:
-	return cmdline_contains_nokaslr(CONFIG_CMDLINE);
-}
-
 static u64 __init get_kaslr_seed(void *fdt)
 {
 	static char const chosen_str[] __initconst = "chosen";
@@ -92,7 +41,7 @@ asmlinkage u64 __init kaslr_early_init(void *fdt)
 {
 	u64 seed, range;
 
-	if (is_kaslr_disabled_cmdline(fdt))
+	if (kaslr_disabled_cmdline())
 		return 0;
 
 	seed = get_kaslr_seed(fdt);
-- 
2.43.0.rc1.413.gea7ed67945-goog


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