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mm: security: Check early if HARDENED_USERCOPY is enabled

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HARDENED_USERCOPY is checked within a function so even if disabled, the
function overhead still exists. Move the static check inline.

This is at best a micro-optimisation and any difference in performance
was within noise but it is relatively consistent with the init_on_*
implementations.

Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20250123221115.19722-4-mgorman@techsingularity.net
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Mel Gorman 2025-01-23 22:11:14 +00:00 committed by Kees Cook
parent d2132f453e
commit 496d2d2388
2 changed files with 15 additions and 7 deletions
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9
include/linux/ucopysize.h
View File

@ -6,14 +6,21 @@
#include <linux/bug.h>
#ifdef CONFIG_HARDENED_USERCOPY
#include <linux/jump_label.h>
extern void __check_object_size(const void *ptr, unsigned long n,
bool to_user);
DECLARE_STATIC_KEY_MAYBE(CONFIG_HARDENED_USERCOPY_DEFAULT_ON,
validate_usercopy_range);
static __always_inline void check_object_size(const void *ptr, unsigned long n,
bool to_user)
{
if (!__builtin_constant_p(n))
if (!__builtin_constant_p(n) &&
static_branch_maybe(CONFIG_HARDENED_USERCOPY_DEFAULT_ON,
&validate_usercopy_range)) {
__check_object_size(ptr, n, to_user);
}
}
#else
static inline void check_object_size(const void *ptr, unsigned long n,

13
mm/usercopy.c
View File

@ -201,7 +201,9 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
}
}
static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks);
DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_HARDENED_USERCOPY_DEFAULT_ON,
validate_usercopy_range);
EXPORT_SYMBOL(validate_usercopy_range);
/*
* Validates that the given object is:
@ -212,9 +214,6 @@ static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks);
*/
void __check_object_size(const void *ptr, unsigned long n, bool to_user)
{
if (static_branch_unlikely(&bypass_usercopy_checks))
return;
/* Skip all tests if size is zero. */
if (!n)
return;
@ -270,8 +269,10 @@ __setup("hardened_usercopy=", parse_hardened_usercopy);
static int __init set_hardened_usercopy(void)
{
if (enable_checks == false)
static_branch_enable(&bypass_usercopy_checks);
if (enable_checks)
static_branch_enable(&validate_usercopy_range);
else
static_branch_disable(&validate_usercopy_range);
return 1;
}