Commit 475ddf1f authored by Kees Cook's avatar Kees Cook
Browse files

fortify: Split reporting and avoid passing string pointer 



In preparation for KUnit testing and further improvements in fortify
failure reporting, split out the report and encode the function and access
failure (read or write overflow) into a single u8 argument. This mainly
ends up saving a tiny bit of space in the data segment. For a defconfig
with FORTIFY_SOURCE enabled:

$ size gcc/vmlinux.before gcc/vmlinux.after
   text  	  data     bss     dec    	    hex filename
26132309        9760658 2195460 38088427        2452eeb gcc/vmlinux.before
26132386        9748382 2195460 38076228        244ff44 gcc/vmlinux.after

Reviewed-by: default avatarAlexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 99db710f

arch/arm/boot/compressed/misc.c

+1 −1
Original line number Diff line number Diff line
@@ -154,7 +154,7 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p, 
		putstr(" done, booting the kernel.\n");

}



void fortify_panic(const char *name)

void __fortify_panic(const u8 reason)

{

	error("detected buffer overflow");

}

arch/arm/boot/compressed/misc.h

+1 −1
Original line number Diff line number Diff line
@@ -10,7 +10,7 @@ void __div0(void); 
void

decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,

		  unsigned long free_mem_ptr_end_p, int arch_id);

void fortify_panic(const char *name);

void __fortify_panic(const u8 reason);

int atags_to_fdt(void *atag_list, void *fdt, int total_space);

uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt);

int do_decompress(u8 *input, int len, u8 *output, void (*error)(char *x));

arch/x86/boot/compressed/misc.c

+1 −1
Original line number Diff line number Diff line
@@ -496,7 +496,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output) 
	return output + entry_offset;

}



void fortify_panic(const char *name)

void __fortify_panic(const u8 reason)

{

	error("detected buffer overflow");

}

include/linux/fortify-string.h

+60 −21
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#ifndef _LINUX_FORTIFY_STRING_H_

#define _LINUX_FORTIFY_STRING_H_



#include <linux/bitfield.h>

#include <linux/bug.h>

#include <linux/const.h>

#include <linux/limits.h>
@@ -9,7 +10,44 @@ 
#define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable

#define __RENAME(x) __asm__(#x)



void fortify_panic(const char *name) __noreturn __cold;

#define FORTIFY_REASON_DIR(r)		FIELD_GET(BIT(0), r)

#define FORTIFY_REASON_FUNC(r)		FIELD_GET(GENMASK(7, 1), r)

#define FORTIFY_REASON(func, write)	(FIELD_PREP(BIT(0), write) | \

					 FIELD_PREP(GENMASK(7, 1), func))



#define fortify_panic(func, write)	\

	__fortify_panic(FORTIFY_REASON(func, write))



#define FORTIFY_READ		 0

#define FORTIFY_WRITE		 1



#define EACH_FORTIFY_FUNC(macro)	\

	macro(strncpy),			\

	macro(strnlen),			\

	macro(strlen),			\

	macro(strscpy),			\

	macro(strlcat),			\

	macro(strcat),			\

	macro(strncat),			\

	macro(memset),			\

	macro(memcpy),			\

	macro(memmove),			\

	macro(memscan),			\

	macro(memcmp),			\

	macro(memchr),			\

	macro(memchr_inv),		\

	macro(kmemdup),			\

	macro(strcpy),			\

	macro(UNKNOWN),



#define MAKE_FORTIFY_FUNC(func)	FORTIFY_FUNC_##func



enum fortify_func {

	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC)

};



void __fortify_report(const u8 reason);

void __fortify_panic(const u8 reason) __cold __noreturn;

void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");

void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");

void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?");
@@ -143,7 +181,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__write_overflow();

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE);

	return __underlying_strncpy(p, q, size);

}
@@ -174,7 +212,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size 
	/* Do not check characters beyond the end of p. */

	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);

	if (p_size <= ret && maxlen != ret)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ);

	return ret;

}
@@ -210,7 +248,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p) 
		return __underlying_strlen(p);

	ret = strnlen(p, p_size);

	if (p_size <= ret)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ);

	return ret;

}
@@ -261,7 +299,7 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO 
	 * p_size.

	 */

	if (len > p_size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE);



	/*

	 * We can now safely call vanilla strscpy because we are protected from:
@@ -319,7 +357,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) 


	/* Give up if string is already overflowed. */

	if (p_size <= p_len)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ);



	if (actual >= avail) {

		copy_len = avail - p_len - 1;
@@ -328,7 +366,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) 


	/* Give up if copy will overflow. */

	if (p_size <= actual)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE);

	__underlying_memcpy(p + p_len, q, copy_len);

	p[actual] = '\0';
@@ -357,7 +395,7 @@ char *strcat(char * const POS p, const char *q) 
	const size_t p_size = __member_size(p);



	if (strlcat(p, q, p_size) >= p_size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE);

	return p;

}
@@ -393,7 +431,7 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun 
	p_len = strlen(p);

	copy_len = strnlen(q, count);

	if (p_size < p_len + copy_len + 1)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE);

	__underlying_memcpy(p + p_len, q, copy_len);

	p[p_len + copy_len] = '\0';

	return p;
@@ -434,7 +472,7 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, 
	 * lengths are unknown.)

	 */

	if (p_size != SIZE_MAX && p_size < size)

		fortify_panic("memset");

		fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE);

}



#define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({	\
@@ -488,7 +526,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, 
					 const size_t q_size,

					 const size_t p_size_field,

					 const size_t q_size_field,

					 const char *func)

					 const u8 func)

{

	if (__builtin_constant_p(size)) {

		/*
@@ -532,9 +570,10 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, 
	 * (The SIZE_MAX test is to optimize away checks where the buffer

	 * lengths are unknown.)

	 */

	if ((p_size != SIZE_MAX && p_size < size) ||

	    (q_size != SIZE_MAX && q_size < size))

		fortify_panic(func);

	if (p_size != SIZE_MAX && p_size < size)

		fortify_panic(func, FORTIFY_WRITE);

	else if (q_size != SIZE_MAX && q_size < size)

		fortify_panic(func, FORTIFY_READ);



	/*

	 * Warn when writing beyond destination field size.
@@ -567,7 +606,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, 
	const size_t __q_size_field = (q_size_field);			\

	WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size,		\

				     __q_size, __p_size_field,		\

				     __q_size_field, #op),		\

				     __q_size_field, FORTIFY_FUNC_ ##op), \

		  #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \

		  __fortify_size,					\

		  "field \"" #p "\" at " FILE_LINE,			\
@@ -634,7 +673,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ);

	return __real_memscan(p, c, size);

}
@@ -651,7 +690,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t 
			__read_overflow2();

	}

	if (p_size < size || q_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ);

	return __underlying_memcmp(p, q, size);

}
@@ -663,7 +702,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ);

	return __underlying_memchr(p, c, size);

}
@@ -675,7 +714,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ);

	return __real_memchr_inv(p, c, size);

}
@@ -688,7 +727,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp 
	if (__compiletime_lessthan(p_size, size))

		__read_overflow();

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ);

	return __real_kmemdup(p, size, gfp);

}
@@ -725,7 +764,7 @@ char *strcpy(char * const POS p, const char * const POS q) 
		__write_overflow();

	/* Run-time check for dynamic size overflow. */

	if (p_size < size)

		fortify_panic(__func__);

		fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE);

	__underlying_memcpy(p, q, size);

	return p;

}

lib/string_helpers.c

+20 −3
Original line number Diff line number Diff line
@@ -1008,10 +1008,27 @@ EXPORT_SYMBOL(__read_overflow2_field); 
void __write_overflow_field(size_t avail, size_t wanted) { }

EXPORT_SYMBOL(__write_overflow_field);



void fortify_panic(const char *name)

static const char * const fortify_func_name[] = {

#define MAKE_FORTIFY_FUNC_NAME(func)	[MAKE_FORTIFY_FUNC(func)] = #func

	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC_NAME)

#undef  MAKE_FORTIFY_FUNC_NAME

};



void __fortify_report(const u8 reason)

{

	const u8 func = FORTIFY_REASON_FUNC(reason);

	const bool write = FORTIFY_REASON_DIR(reason);

	const char *name;



	name = fortify_func_name[umin(func, FORTIFY_FUNC_UNKNOWN)];

	WARN(1, "%s: detected buffer %s overflow\n", name, str_read_write(!write));

}

EXPORT_SYMBOL(__fortify_report);



void __fortify_panic(const u8 reason)

{

	pr_emerg("detected buffer overflow in %s\n", name);

	__fortify_report(reason);

	BUG();

}

EXPORT_SYMBOL(fortify_panic);

EXPORT_SYMBOL(__fortify_panic);

#endif /* CONFIG_FORTIFY_SOURCE */