Merge branch 'for-6.17-hash_pointers' into for-linus (731ae3ad) · Commits · git / linux-net

Documentation/admin-guide/kernel-parameters.txt

+26 −12

Original line number	Diff line number	Diff line
		@@ -1798,6 +1798,27 @@
		backtraces on all cpus.
		Format: 0 \| 1

		hash_pointers=
		[KNL,EARLY]
		By default, when pointers are printed to the console
		or buffers via the %p format string, that pointer is
		"hashed", i.e. obscured by hashing the pointer value.
		This is a security feature that hides actual kernel
		addresses from unprivileged users, but it also makes
		debugging the kernel more difficult since unequal
		pointers can no longer be compared. The choices are:
		Format: { auto \| always \| never }
		Default: auto

		auto - Hash pointers unless slab_debug is enabled.
		always - Always hash pointers (even if slab_debug is
		enabled).
		never - Never hash pointers. This option should only
		be specified when debugging the kernel. Do
		not use on production kernels. The boot
		param "no_hash_pointers" is an alias for
		this mode.

		hashdist= [KNL,NUMA] Large hashes allocated during boot
		are distributed across NUMA nodes. Defaults on
		for 64-bit NUMA, off otherwise.
		@@ -4120,18 +4141,7 @@

		no_hash_pointers
		[KNL,EARLY]
		Force pointers printed to the console or buffers to be
		unhashed. By default, when a pointer is printed via %p
		format string, that pointer is "hashed", i.e. obscured
		by hashing the pointer value. This is a security feature
		that hides actual kernel addresses from unprivileged
		users, but it also makes debugging the kernel more
		difficult since unequal pointers can no longer be
		compared. However, if this command-line option is
		specified, then all normal pointers will have their true
		value printed. This option should only be specified when
		debugging the kernel. Please do not use on production
		kernels.
		Alias for "hash_pointers=never".

		nohibernate [HIBERNATION] Disable hibernation and resume.

		@@ -6481,6 +6491,10 @@
		Documentation/mm/slub.rst.
		(slub_debug legacy name also accepted for now)

		Using this option implies the "no_hash_pointers"
		option which can be undone by adding the
		"hash_pointers=always" option.

		slab_max_order= [MM]
		Determines the maximum allowed order for slabs.
		A high setting may cause OOMs due to memory

include/linux/sprintf.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -22,7 +22,7 @@ __scanf(2, 0) int vsscanf(const char , const char , va_list);

		/* These are for specific cases, do not use without real need */
		extern bool no_hash_pointers;
		int no_hash_pointers_enable(char *str);
		void hash_pointers_finalize(bool slub_debug);

		/* Used for Rust formatting ('%pA') */
		char rust_fmt_argument(char buf, char end, const void ptr);

lib/vsprintf.c

+57 −4

Original line number	Diff line number	Diff line
		@@ -60,6 +60,20 @@
		bool no_hash_pointers __ro_after_init;
		EXPORT_SYMBOL_GPL(no_hash_pointers);

		/*
		* Hashed pointers policy selected by "hash_pointers=..." boot param
		*
		* `auto` - Hashed pointers enabled unless disabled by slub_debug_enabled=true
		* `always` - Hashed pointers enabled unconditionally
		* `never` - Hashed pointers disabled unconditionally
		*/
		enum hash_pointers_policy {
		HASH_PTR_AUTO = 0,
		HASH_PTR_ALWAYS,
		HASH_PTR_NEVER
		};
		static enum hash_pointers_policy hash_pointers_mode __initdata;

		noinline
		static unsigned long long simple_strntoull(const char startp, char *endp, unsigned int base, size_t max_chars)
		{
		@@ -2270,12 +2284,23 @@ char resource_or_range(const char fmt, char buf, char end, void *ptr,
		return resource_string(buf, end, ptr, spec, fmt);
		}

		int __init no_hash_pointers_enable(char *str)
		void __init hash_pointers_finalize(bool slub_debug)
		{
		if (no_hash_pointers)
		return 0;

		switch (hash_pointers_mode) {
		case HASH_PTR_ALWAYS:
		no_hash_pointers = false;
		break;
		case HASH_PTR_NEVER:
		no_hash_pointers = true;
		break;
		case HASH_PTR_AUTO:
		default:
		no_hash_pointers = slub_debug;
		break;
		}

		if (!no_hash_pointers)
		return;

		pr_warn("**********************************************************\n");
		pr_warn(" NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE \n");
		@@ -2288,11 +2313,39 @@ int __init no_hash_pointers_enable(char *str)
		pr_warn(" the kernel, report this immediately to your system \n");
		pr_warn(" administrator! \n");
		pr_warn(" \n");
		pr_warn(" Use hash_pointers=always to force this mode off \n");
		pr_warn(" \n");
		pr_warn(" NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE \n");
		pr_warn("**********************************************************\n");
		}

		static int __init hash_pointers_mode_parse(char *str)
		{
		if (!str) {
		pr_warn("Hash pointers mode empty; falling back to auto.\n");
		hash_pointers_mode = HASH_PTR_AUTO;
		} else if (strncmp(str, "auto", 4) == 0) {
		pr_info("Hash pointers mode set to auto.\n");
		hash_pointers_mode = HASH_PTR_AUTO;
		} else if (strncmp(str, "never", 5) == 0) {
		pr_info("Hash pointers mode set to never.\n");
		hash_pointers_mode = HASH_PTR_NEVER;
		} else if (strncmp(str, "always", 6) == 0) {
		pr_info("Hash pointers mode set to always.\n");
		hash_pointers_mode = HASH_PTR_ALWAYS;
		} else {
		pr_warn("Unknown hash_pointers mode '%s' specified; assuming auto.\n", str);
		hash_pointers_mode = HASH_PTR_AUTO;
		}

		return 0;
		}
		early_param("hash_pointers", hash_pointers_mode_parse);

		static int __init no_hash_pointers_enable(char *str)
		{
		return hash_pointers_mode_parse("never");
		}
		early_param("no_hash_pointers", no_hash_pointers_enable);

		/*

mm/slub.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -6314,9 +6314,8 @@ void __init kmem_cache_init(void)
		if (debug_guardpage_minorder())
		slub_max_order = 0;

		/* Print slub debugging pointers without hashing */
		if (__slub_debug_enabled())
		no_hash_pointers_enable(NULL);
		/* Inform pointer hashing choice about slub debugging state. */
		hash_pointers_finalize(__slub_debug_enabled());

		kmem_cache_node = &boot_kmem_cache_node;
		kmem_cache = &boot_kmem_cache;