arm64: fix rodata=full

On arm64, "rodata=full" has been suppored (but not documented) since
commit:

  c55191e96caa9d78 ("arm64: mm: apply r/o permissions of VM areas to its linear alias as well")

As it's necessary to determine the rodata configuration early during
boot, arm64 has an early_param() handler for this, whereas init/main.c
has a __setup() handler which is run later.

Unfortunately, this split meant that since commit:

  f9a40b0890658330 ("init/main.c: return 1 from handled __setup() functions")

... passing "rodata=full" would result in a spurious warning from the
__setup() handler (though RO permissions would be configured
appropriately).

Further, "rodata=full" has been broken since commit:

  0d6ea3ac94ca77c5 ("lib/kstrtox.c: add "false"/"true" support to kstrtobool()")

... which caused strtobool() to parse "full" as false (in addition to
many other values not documented for the "rodata=" kernel parameter.

This patch fixes this breakage by:

* Moving the core parameter parser to an __early_param(), such that it
  is available early.

* Adding an (optional) arch hook which arm64 can use to parse "full".

* Updating the documentation to mention that "full" is valid for arm64.

* Having the core parameter parser handle "on" and "off" explicitly,
  such that any undocumented values (e.g. typos such as "ful") are
  reported as errors rather than being silently accepted.

Note that __setup() and early_param() have opposite conventions for
their return values, where __setup() uses 1 to indicate a parameter was
handled and early_param() uses 0 to indicate a parameter was handled.

Fixes: f9a40b089065 ("init/main.c: return 1 from handled __setup() functions")
Fixes: 0d6ea3ac94ca ("lib/kstrtox.c: add "false"/"true" support to kstrtobool()")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jagdish Gediya <jvgediya@linux.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220817154022.3974645-1-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 15 insertions, 3 deletions

diff --git a/init/main.c b/init/main.c
index 91642a4e69be..1fe7942f5d4a 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1446,13 +1446,25 @@ static noinline void __init kernel_init_freeable(void);
 
 #if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)
 bool rodata_enabled __ro_after_init = true;
+
+#ifndef arch_parse_debug_rodata
+static inline bool arch_parse_debug_rodata(char *str) { return false; }
+#endif
+
 static int __init set_debug_rodata(char *str)
 {
-	if (strtobool(str, &rodata_enabled))
+	if (arch_parse_debug_rodata(str))
+		return 0;
+
+	if (str && !strcmp(str, "on"))
+		rodata_enabled = true;
+	else if (str && !strcmp(str, "off"))
+		rodata_enabled = false;
+	else
 		pr_warn("Invalid option string for rodata: '%s'\n", str);
-	return 1;
+	return 0;
 }
-__setup("rodata=", set_debug_rodata);
+early_param("rodata", set_debug_rodata);
 #endif
 
 #ifdef CONFIG_STRICT_KERNEL_RWX