linux-kernel - [PATCH v3 15/60] arm64: kernel: Don't rely on objcopy to make code under pi/ _

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Message-Id: <20230307140522.2311461-16-ardb@kernel.org>
Date:   Tue,  7 Mar 2023 15:04:37 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ryan Roberts <ryan.roberts@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH v3 15/60] arm64: kernel: Don't rely on objcopy to make code under pi/ __init

We will add some code under pi/ that contains global variables that
should not end up in __initdata, as they will not be writable via the
initial ID map. So only rely on objcopy for making the libfdt code
__init, and use explicit annotations for the rest.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/kernel/pi/Makefile      |  6 ++++--
 arch/arm64/kernel/pi/kaslr_early.c | 16 +++++++++-------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/pi/Makefile b/arch/arm64/kernel/pi/Makefile
index bc32a431fe35e6f4..2bbe866417d453ff 100644
--- a/arch/arm64/kernel/pi/Makefile
+++ b/arch/arm64/kernel/pi/Makefile
@@ -28,11 +28,13 @@ quiet_cmd_piobjcopy = $(quiet_cmd_objcopy)
       cmd_piobjcopy = $(cmd_objcopy) && $(obj)/relacheck $(@) $(<)
 
 $(obj)/%.pi.o: OBJCOPYFLAGS := --prefix-symbols=__pi_ \
-			       --remove-section=.note.gnu.property \
-			       --prefix-alloc-sections=.init
+			       --remove-section=.note.gnu.property
 $(obj)/%.pi.o: $(obj)/%.o $(obj)/relacheck FORCE
 	$(call if_changed,piobjcopy)
 
+# ensure that all the lib- code ends up as __init code and data
+$(obj)/lib-%.pi.o: OBJCOPYFLAGS += --prefix-alloc-sections=.init
+
 $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
index b9e0bb4bc6a9766f..167081b30a152d0a 100644
--- a/arch/arm64/kernel/pi/kaslr_early.c
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -17,7 +17,7 @@
 #include <asm/pgtable.h>
 
 /* taken from lib/string.c */
-static char *__strstr(const char *s1, const char *s2)
+static char *__init __strstr(const char *s1, const char *s2)
 {
 	size_t l1, l2;
 
@@ -33,7 +33,7 @@ static char *__strstr(const char *s1, const char *s2)
 	}
 	return NULL;
 }
-static bool cmdline_contains_nokaslr(const u8 *cmdline)
+static bool __init cmdline_contains_nokaslr(const u8 *cmdline)
 {
 	const u8 *str;
 
@@ -41,7 +41,7 @@ static bool cmdline_contains_nokaslr(const u8 *cmdline)
 	return str == cmdline || (str > cmdline && *(str - 1) == ' ');
 }
 
-static bool is_kaslr_disabled_cmdline(void *fdt)
+static bool __init is_kaslr_disabled_cmdline(void *fdt)
 {
 	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
 		int node;
@@ -67,17 +67,19 @@ static bool is_kaslr_disabled_cmdline(void *fdt)
 	return cmdline_contains_nokaslr(CONFIG_CMDLINE);
 }
 
-static u64 get_kaslr_seed(void *fdt)
+static u64 __init get_kaslr_seed(void *fdt)
 {
+	static char const chosen_str[] __initconst = "chosen";
+	static char const seed_str[] __initconst = "kaslr-seed";
 	int node, len;
 	fdt64_t *prop;
 	u64 ret;
 
-	node = fdt_path_offset(fdt, "/chosen");
+	node = fdt_path_offset(fdt, chosen_str);
 	if (node < 0)
 		return 0;
 
-	prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
+	prop = fdt_getprop_w(fdt, node, seed_str, &len);
 	if (!prop || len != sizeof(u64))
 		return 0;
 
@@ -86,7 +88,7 @@ static u64 get_kaslr_seed(void *fdt)
 	return ret;
 }
 
-asmlinkage u64 kaslr_early_init(void *fdt)
+asmlinkage u64 __init kaslr_early_init(void *fdt)
 {
 	u64 seed, range;
 
-- 
2.39.2