s390/fpu: make use of __uninitialized macro

Code sections in s390 specific kernel code which use floating point or
vector registers all come with a 520 byte stack variable to save already in
use registers, if required.

With INIT_STACK_ALL_PATTERN or INIT_STACK_ALL_ZERO enabled this variable
will always be initialized on function entry in addition to saving register
contents, which contradicts the intention (performance improvement) of such
code sections.

Therefore provide a DECLARE_KERNEL_FPU_ONSTACK() macro which provides
struct kernel_fpu variables with an __uninitialized attribute, and convert
all existing code to use this.

This way only this specific type of stack variable will not be initialized,
regardless of config options.
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240205154844.3757121-3-hca@linux.ibm.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/crypto/chacha-glue.c

@@ -22,7 +22,7 @@ static void chacha20_crypt_s390(u32 *state, u8 *dst, const u8 *src,
 				unsigned int nbytes, const u32 *key,
 				u32 *counter)
 {
-	struct kernel_fpu vxstate;
+	DECLARE_KERNEL_FPU_ONSTACK(vxstate);
 
 	kernel_fpu_begin(&vxstate, KERNEL_VXR);
 	chacha20_vx(dst, src, nbytes, key, counter);

arch/s390/crypto/crc32-vx.c

@@ -49,8 +49,8 @@ u32 crc32c_le_vgfm_16(u32 crc, unsigned char const *buf, size_t size);
 	static u32 __pure ___fname(u32 crc,				    \
 				unsigned char const *data, size_t datalen)  \
 	{								    \
-		struct kernel_fpu vxstate;				    \
 		unsigned long prealign, aligned, remaining;		    \
+		DECLARE_KERNEL_FPU_ONSTACK(vxstate);			    \
 									    \
 		if (datalen < VX_MIN_LEN + VX_ALIGN_MASK)		    \
 			return ___crc32_sw(crc, data, datalen);		    \

arch/s390/include/asm/fpu/types.h

@@ -35,4 +35,7 @@ struct kernel_fpu {
 	};
 };
 
+#define DECLARE_KERNEL_FPU_ONSTACK(name)	\
+	struct kernel_fpu name __uninitialized
+
 #endif /* _ASM_S390_FPU_TYPES_H */

arch/s390/kernel/sysinfo.c

@@ -426,9 +426,9 @@ subsys_initcall(create_proc_service_level);
  */
 void s390_adjust_jiffies(void)
 {
+	DECLARE_KERNEL_FPU_ONSTACK(fpu);
 	struct sysinfo_1_2_2 *info;
 	unsigned long capability;
-	struct kernel_fpu fpu;
 
 	info = (void *) get_zeroed_page(GFP_KERNEL);
 	if (!info)

lib/raid6/s390vx.uc

@@ -81,7 +81,7 @@ static inline void COPY_VEC(int x, int y)
 
 static void raid6_s390vx$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
 {
-	struct kernel_fpu vxstate;
+	DECLARE_KERNEL_FPU_ONSTACK(vxstate);
 	u8 **dptr, *p, *q;
 	int d, z, z0;
 
@@ -114,7 +114,7 @@ static void raid6_s390vx$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
 static void raid6_s390vx$#_xor_syndrome(int disks, int start, int stop,
 					size_t bytes, void **ptrs)
 {
-	struct kernel_fpu vxstate;
+	DECLARE_KERNEL_FPU_ONSTACK(vxstate);
 	u8 **dptr, *p, *q;
 	int d, z, z0;