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fortify: Explicitly check bounds are compile-time constants

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In preparation for replacing __builtin_object_size() with
__builtin_dynamic_object_size(), all the compile-time size checks
need to check that the bounds comparisons are, in fact, known at
compile-time. Enforce what was guaranteed with __bos(). In other words,
since all uses of __bos() were constant expressions, it was not required
to test for this. When these change to __bdos(), they _may_ be constant
expressions, and the checks are only valid when the prior condition
holds. This results in no binary differences.

Cc: linux-hardening@vger.kernel.org
Link: https://lore.kernel.org/lkml/20220920192202.190793-3-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2022-09-19 16:33:33 -07:00
parent 3e1730842f
commit fa35198f39
1 changed files with 30 additions and 19 deletions
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49
include/linux/fortify-string.h
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@ -80,6 +80,11 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
#define POS __pass_object_size(1)
#define POS0 __pass_object_size(0)
#define __compiletime_lessthan(bounds, length) ( \
__builtin_constant_p((bounds) < (length)) && \
(bounds) < (length) \
)
/**
* strncpy - Copy a string to memory with non-guaranteed NUL padding
*
@ -117,7 +122,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
{
size_t p_size = __builtin_object_size(p, 1);
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__write_overflow();
if (p_size < size)
fortify_panic(__func__);
@ -224,7 +229,7 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s
* If size can be known at compile time and is greater than
* p_size, generate a compile time write overflow error.
*/
if (__builtin_constant_p(size) && size > p_size)
if (__compiletime_lessthan(p_size, size))
__write_overflow();
/*
@ -281,15 +286,16 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
/*
* Length argument is a constant expression, so we
* can perform compile-time bounds checking where
* buffer sizes are known.
* buffer sizes are also known at compile time.
*/
/* Error when size is larger than enclosing struct. */
if (p_size > p_size_field && p_size < size)
if (__compiletime_lessthan(p_size_field, p_size) &&
__compiletime_lessthan(p_size, size))
__write_overflow();
/* Warn when write size is larger than dest field. */
if (p_size_field < size)
if (__compiletime_lessthan(p_size_field, size))
__write_overflow_field(p_size_field, size);
}
/*
@ -365,25 +371,28 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
/*
* Length argument is a constant expression, so we
* can perform compile-time bounds checking where
* buffer sizes are known.
* buffer sizes are also known at compile time.
*/
/* Error when size is larger than enclosing struct. */
if (p_size > p_size_field && p_size < size)
if (__compiletime_lessthan(p_size_field, p_size) &&
__compiletime_lessthan(p_size, size))
__write_overflow();
if (q_size > q_size_field && q_size < size)
if (__compiletime_lessthan(q_size_field, q_size) &&
__compiletime_lessthan(q_size, size))
__read_overflow2();
/* Warn when write size argument larger than dest field. */
if (p_size_field < size)
if (__compiletime_lessthan(p_size_field, size))
__write_overflow_field(p_size_field, size);
/*
* Warn for source field over-read when building with W=1
* or when an over-write happened, so both can be fixed at
* the same time.
*/
if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) &&
q_size_field < size)
if ((IS_ENABLED(KBUILD_EXTRA_WARN1) ||
__compiletime_lessthan(p_size_field, size)) &&
__compiletime_lessthan(q_size_field, size))
__read_overflow2_field(q_size_field, size);
}
/*
@ -494,7 +503,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
{
size_t p_size = __builtin_object_size(p, 0);
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__read_overflow();
if (p_size < size)
fortify_panic(__func__);
@ -508,9 +517,9 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
size_t q_size = __builtin_object_size(q, 0);
if (__builtin_constant_p(size)) {
if (p_size < size)
if (__compiletime_lessthan(p_size, size))
__read_overflow();
if (q_size < size)
if (__compiletime_lessthan(q_size, size))
__read_overflow2();
}
if (p_size < size || q_size < size)
@ -523,7 +532,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
{
size_t p_size = __builtin_object_size(p, 0);
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__read_overflow();
if (p_size < size)
fortify_panic(__func__);
@ -535,7 +544,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
{
size_t p_size = __builtin_object_size(p, 0);
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__read_overflow();
if (p_size < size)
fortify_panic(__func__);
@ -547,7 +556,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
{
size_t p_size = __builtin_object_size(p, 0);
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__read_overflow();
if (p_size < size)
fortify_panic(__func__);
@ -563,11 +572,13 @@ char *strcpy(char * const POS p, const char * const POS q)
size_t size;
/* If neither buffer size is known, immediately give up. */
if (p_size == SIZE_MAX && q_size == SIZE_MAX)
if (__builtin_constant_p(p_size) &&
__builtin_constant_p(q_size) &&
p_size == SIZE_MAX && q_size == SIZE_MAX)
return __underlying_strcpy(p, q);
size = strlen(q) + 1;
/* Compile-time check for const size overflow. */
if (__builtin_constant_p(size) && p_size < size)
if (__compiletime_lessthan(p_size, size))
__write_overflow();
/* Run-time check for dynamic size overflow. */
if (p_size < size)