[PATCH v2] usercopy: Check valid lifetime via stack depth
Kees Cook
keescook at chromium.org
Thu Feb 24 17:03:42 AEDT 2022
Under CONFIG_HARDENED_USERCOPY=y, when exact stack frame boundary checking
is not available (i.e. everything except x86 with FRAME_POINTER), check
a stack object as being at least "current depth valid", in the sense
that any object within the stack region but not between start-of-stack
and current_stack_pointer should be considered unavailable (i.e. its
lifetime is from a call no longer present on the stack).
Introduce ARCH_HAS_CURRENT_STACK_POINTER to track which architectures
have actually implemented the common global register alias.
Additionally report usercopy bounds checking failures with an offset
from current_stack_pointer, which may assist with diagnosing failures.
The LKDTM USERCOPY_STACK_FRAME_TO and USERCOPY_STACK_FRAME_FROM tests
(once slightly adjusted in a separate patch) will pass again with
this fixed.
Cc: Matthew Wilcox (Oracle) <willy at infradead.org>
Cc: Josh Poimboeuf <jpoimboe at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: linux-mm at kvack.org
Reported-by: Muhammad Usama Anjum <usama.anjum at collabora.com>
Signed-off-by: Kees Cook <keescook at chromium.org>
---
v1: https://lore.kernel.org/all/20220216201449.2087956-1-keescook@chromium.org/
v2: adjust for only some archs having current_stack_pointer
---
arch/arm/Kconfig | 1 +
arch/arm64/Kconfig | 1 +
arch/powerpc/Kconfig | 1 +
arch/s390/Kconfig | 1 +
arch/sh/Kconfig | 1 +
arch/x86/Kconfig | 1 +
mm/usercopy.c | 41 ++++++++++++++++++++++++++++++++++++++---
7 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 4c97cb40eebb..a7a09eef1852 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -5,6 +5,7 @@ config ARM
select ARCH_32BIT_OFF_T
select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE if HAVE_KRETPROBES && FRAME_POINTER && !ARM_UNWIND
select ARCH_HAS_BINFMT_FLAT
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL if MMU
select ARCH_HAS_DMA_WRITE_COMBINE if !ARM_DMA_MEM_BUFFERABLE
select ARCH_HAS_ELF_RANDOMIZE
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f2b5a4abef21..b8ab790555c8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -18,6 +18,7 @@ config ARM64
select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
select ARCH_HAS_CACHE_LINE_SIZE
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL
select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DMA_PREP_COHERENT
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b779603978e1..7e7387bd7d53 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -108,6 +108,7 @@ config PPC
select ARCH_ENABLE_MEMORY_HOTPLUG
select ARCH_ENABLE_MEMORY_HOTREMOVE
select ARCH_HAS_COPY_MC if PPC64
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL
select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DEBUG_WX if STRICT_KERNEL_RWX
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index be9f39fd06df..4845ab549dd1 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -60,6 +60,7 @@ config S390
select ARCH_ENABLE_MEMORY_HOTPLUG if SPARSEMEM
select ARCH_ENABLE_MEMORY_HOTREMOVE
select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DEBUG_WX
select ARCH_HAS_DEVMEM_IS_ALLOWED
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 2474a04ceac4..1c2b53bf3093 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -7,6 +7,7 @@ config SUPERH
select ARCH_HAVE_CUSTOM_GPIO_H
select ARCH_HAVE_NMI_SAFE_CMPXCHG if (GUSA_RB || CPU_SH4A)
select ARCH_HAS_BINFMT_FLAT if !MMU
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_GIGANTIC_PAGE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_PTE_SPECIAL
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9f5bd41bf660..90494fba3620 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -69,6 +69,7 @@ config X86
select ARCH_ENABLE_THP_MIGRATION if X86_64 && TRANSPARENT_HUGEPAGE
select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
select ARCH_HAS_CACHE_LINE_SIZE
+ select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL
select ARCH_HAS_DEBUG_VM_PGTABLE if !X86_PAE
select ARCH_HAS_DEVMEM_IS_ALLOWED
diff --git a/mm/usercopy.c b/mm/usercopy.c
index d0d268135d96..5d28725af95f 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -22,6 +22,30 @@
#include <asm/sections.h>
#include "slab.h"
+/*
+ * Only called if obj is within stack/stackend bounds. Determine if within
+ * current stack depth.
+ */
+static inline int check_stack_object_depth(const void *obj,
+ unsigned long len)
+{
+#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER
+#ifndef CONFIG_STACK_GROWSUP
+ const void * const high = stackend;
+ const void * const low = (void *)current_stack_pointer;
+#else
+ const void * const high = (void *)current_stack_pointer;
+ const void * const low = stack;
+#endif
+
+ /* Reject: object not within current stack depth. */
+ if (obj < low || high < obj + len)
+ return BAD_STACK;
+
+#endif
+ return GOOD_STACK;
+}
+
/*
* Checks if a given pointer and length is contained by the current
* stack frame (if possible).
@@ -29,7 +53,7 @@
* Returns:
* NOT_STACK: not at all on the stack
* GOOD_FRAME: fully within a valid stack frame
- * GOOD_STACK: fully on the stack (when can't do frame-checking)
+ * GOOD_STACK: within the current stack (when can't frame-check exactly)
* BAD_STACK: error condition (invalid stack position or bad stack frame)
*/
static noinline int check_stack_object(const void *obj, unsigned long len)
@@ -55,7 +79,8 @@ static noinline int check_stack_object(const void *obj, unsigned long len)
if (ret)
return ret;
- return GOOD_STACK;
+ /* Finally, check stack depth if possible. */
+ return check_stack_object_depth(obj, len);
}
/*
@@ -280,7 +305,17 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user)
*/
return;
default:
- usercopy_abort("process stack", NULL, to_user, 0, n);
+ usercopy_abort("process stack", NULL, to_user,
+#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER
+# ifndef CONFIG_STACK_GROWSUP
+ (void *)current_stack_pointer - ptr,
+# else
+ ptr - (void *)current_stack_pointer,
+# endif
+#else
+ 0,
+#endif
+ n);
}
/* Check for bad heap object. */
--
2.30.2
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