stackleak: Rename STACKLEAK to KSTACK_ERASE

In preparation for adding Clang sanitizer coverage stack depth tracking
that can support stack depth callbacks:

- Add the new top-level CONFIG_KSTACK_ERASE option which will be
  implemented either with the stackleak GCC plugin, or with the Clang
  stack depth callback support.
- Rename CONFIG_GCC_PLUGIN_STACKLEAK as needed to CONFIG_KSTACK_ERASE,
  but keep it for anything specific to the GCC plugin itself.
- Rename all exposed "STACKLEAK" names and files to "KSTACK_ERASE" (named
  for what it does rather than what it protects against), but leave as
  many of the internals alone as possible to avoid even more churn.

While here, also split "prev_lowest_stack" into CONFIG_KSTACK_ERASE_METRICS,
since that's the only place it is referenced from.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250717232519.2984886-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

Author: kees

Documentation/admin-guide/sysctl/kernel.rst

@@ -1465,15 +1465,15 @@ stack_erasing
 =============
 
 This parameter can be used to control kernel stack erasing at the end
-of syscalls for kernels built with ``CONFIG_GCC_PLUGIN_STACKLEAK``.
+of syscalls for kernels built with ``CONFIG_KSTACK_ERASE``.
 
 That erasing reduces the information which kernel stack leak bugs
 can reveal and blocks some uninitialized stack variable attacks.
 The tradeoff is the performance impact: on a single CPU system kernel
 compilation sees a 1% slowdown, other systems and workloads may vary.
 
 = ====================================================================
-0 Kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
+0 Kernel stack erasing is disabled, KSTACK_ERASE_METRICS are not updated.
 1 Kernel stack erasing is enabled (default), it is performed before
   returning to the userspace at the end of syscalls.
 = ====================================================================

Documentation/arch/x86/x86_64/mm.rst

@@ -176,5 +176,5 @@ Be very careful vs. KASLR when changing anything here. The KASLR address
 range must not overlap with anything except the KASAN shadow area, which is
 correct as KASAN disables KASLR.
 
-For both 4- and 5-level layouts, the STACKLEAK_POISON value in the last 2MB
+For both 4- and 5-level layouts, the KSTACK_ERASE_POISON value in the last 2MB
 hole: ffffffffffff4111

Documentation/security/self-protection.rst

@@ -303,7 +303,7 @@ Memory poisoning
 
 When releasing memory, it is best to poison the contents, to avoid reuse
 attacks that rely on the old contents of memory. E.g., clear stack on a
-syscall return (``CONFIG_GCC_PLUGIN_STACKLEAK``), wipe heap memory on a
+syscall return (``CONFIG_KSTACK_ERASE``), wipe heap memory on a
 free. This frustrates many uninitialized variable attacks, stack content
 exposures, heap content exposures, and use-after-free attacks.
 

Documentation/translations/zh_CN/security/self-protection.rst

@@ -259,7 +259,7 @@ KALLSYSM，则会直接打印原始地址。
 --------
 
 在释放内存时，最好对内存内容进行清除处理，以防止攻击者重用内存中以前
-的内容。例如，在系统调用返回时清除堆栈（CONFIG_GCC_PLUGIN_STACKLEAK）,
+的内容。例如，在系统调用返回时清除堆栈（CONFIG_KSTACK_ERASE）,
 在释放堆内容是清除其内容。这有助于防止许多未初始化变量攻击、堆栈内容
 泄露、堆内容泄露以及使用后释放攻击（user-after-free）。
 

MAINTAINERS

@@ -9992,8 +9992,6 @@ L:	linux-hardening@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
 F:	Documentation/kbuild/gcc-plugins.rst
-F:	include/linux/stackleak.h
-F:	kernel/stackleak.c
 F:	scripts/Makefile.gcc-plugins
 F:	scripts/gcc-plugins/
 
@@ -13087,10 +13085,12 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/har
 F:	Documentation/ABI/testing/sysfs-kernel-oops_count
 F:	Documentation/ABI/testing/sysfs-kernel-warn_count
 F:	arch/*/configs/hardening.config
+F:	include/linux/kstack_erase.h
 F:	include/linux/overflow.h
 F:	include/linux/randomize_kstack.h
 F:	include/linux/ucopysize.h
 F:	kernel/configs/hardening.config
+F:	kernel/kstack_erase.c
 F:	lib/tests/randstruct_kunit.c
 F:	lib/tests/usercopy_kunit.c
 F:	mm/usercopy.c

arch/Kconfig

@@ -630,11 +630,11 @@ config SECCOMP_CACHE_DEBUG
 
 	  If unsure, say N.
 
-config HAVE_ARCH_STACKLEAK
+config HAVE_ARCH_KSTACK_ERASE
 	bool
 	help
 	  An architecture should select this if it has the code which
-	  fills the used part of the kernel stack with the STACKLEAK_POISON
+	  fills the used part of the kernel stack with the KSTACK_ERASE_POISON
 	  value before returning from system calls.
 
 config HAVE_STACKPROTECTOR

arch/arm/Kconfig

@@ -87,11 +87,11 @@ config ARM
 	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
 	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
 	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
+	select HAVE_ARCH_KSTACK_ERASE
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
 	select HAVE_ARCH_PFN_VALID
 	select HAVE_ARCH_SECCOMP
 	select HAVE_ARCH_SECCOMP_FILTER if AEABI && !OABI_COMPAT
-	select HAVE_ARCH_STACKLEAK
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARM_LPAE

arch/arm/boot/compressed/Makefile

@@ -9,7 +9,7 @@ OBJS		=
 
 HEAD	= head.o
 OBJS	+= misc.o decompress.o
-CFLAGS_decompress.o += $(DISABLE_STACKLEAK_PLUGIN)
+CFLAGS_decompress.o += $(DISABLE_KSTACK_ERASE)
 ifeq ($(CONFIG_DEBUG_UNCOMPRESS),y)
 OBJS	+= debug.o
 AFLAGS_head.o += -DDEBUG

arch/arm/kernel/entry-common.S

@@ -119,7 +119,7 @@ no_work_pending:
 
 	ct_user_enter save = 0
 
-#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+#ifdef CONFIG_KSTACK_ERASE
 	bl	stackleak_erase_on_task_stack
 #endif
 	restore_user_regs fast = 0, offset = 0

arch/arm64/Kconfig

@@ -187,12 +187,12 @@ config ARM64
 	select HAVE_ARCH_KCSAN if EXPERT
 	select HAVE_ARCH_KFENCE
 	select HAVE_ARCH_KGDB
+	select HAVE_ARCH_KSTACK_ERASE
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_SECCOMP_FILTER
-	select HAVE_ARCH_STACKLEAK
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE