fork: Add generic vmalloced stack support

[karo-tx-linux.git] / arch / Kconfig

diff --git a/arch/Kconfig b/arch/Kconfig
index bd8056b5b246058a8c06190811f875a00f30df8d..9ecf9f6f9e15b2093560311da73351958dc444a6 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -461,6 +461,15 @@ config CC_STACKPROTECTOR_STRONG
 
 endchoice
 
+config HAVE_ARCH_WITHIN_STACK_FRAMES
+       bool
+       help
+         An architecture should select this if it can walk the kernel stack
+         frames to determine if an object is part of either the arguments
+         or local variables (i.e. that it excludes saved return addresses,
+         and similar) by implementing an inline arch_within_stack_frames(),
+         which is used by CONFIG_HARDENED_USERCOPY.
+
 config HAVE_CONTEXT_TRACKING
        bool
        help
@@ -698,4 +707,38 @@ config ARCH_NO_COHERENT_DMA_MMAP
 config CPU_NO_EFFICIENT_FFS
        def_bool n
 
+config HAVE_ARCH_VMAP_STACK
+       def_bool n
+       help
+         An arch should select this symbol if it can support kernel stacks
+         in vmalloc space.  This means:
+
+         - vmalloc space must be large enough to hold many kernel stacks.
+           This may rule out many 32-bit architectures.
+
+         - Stacks in vmalloc space need to work reliably.  For example, if
+           vmap page tables are created on demand, either this mechanism
+           needs to work while the stack points to a virtual address with
+           unpopulated page tables or arch code (switch_to() and switch_mm(),
+           most likely) needs to ensure that the stack's page table entries
+           are populated before running on a possibly unpopulated stack.
+
+         - If the stack overflows into a guard page, something reasonable
+           should happen.  The definition of "reasonable" is flexible, but
+           instantly rebooting without logging anything would be unfriendly.
+
+config VMAP_STACK
+       default y
+       bool "Use a virtually-mapped stack"
+       depends on HAVE_ARCH_VMAP_STACK && !KASAN
+       ---help---
+         Enable this if you want the use virtually-mapped kernel stacks
+         with guard pages.  This causes kernel stack overflows to be
+         caught immediately rather than causing difficult-to-diagnose
+         corruption.
+
+         This is presently incompatible with KASAN because KASAN expects
+         the stack to map directly to the KASAN shadow map using a formula
+         that is incorrect if the stack is in vmalloc space.
+
 source "kernel/gcov/Kconfig"