linux-kernel - [PATCH 2/2] s390/fpu: make use of _

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Message-Id: <20240205154844.3757121-3-hca@linux.ibm.com>
Date: Mon,  5 Feb 2024 16:48:44 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Kees Cook <keescook@...omium.org>, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: [PATCH 2/2] 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 intend (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.

Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
---
 arch/s390/crypto/chacha-glue.c    | 2 +-
 arch/s390/crypto/crc32-vx.c       | 2 +-
 arch/s390/include/asm/fpu/types.h | 3 +++
 arch/s390/kernel/sysinfo.c        | 2 +-
 lib/raid6/s390vx.uc               | 4 ++--
 5 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/s390/crypto/chacha-glue.c b/arch/s390/crypto/chacha-glue.c
index ed9959e6f714..a823132fc563 100644
--- a/arch/s390/crypto/chacha-glue.c
+++ b/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);
diff --git a/arch/s390/crypto/crc32-vx.c b/arch/s390/crypto/crc32-vx.c
index 017143e9cef7..6ae3e3ff5b0a 100644
--- a/arch/s390/crypto/crc32-vx.c
+++ b/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);		    \
diff --git a/arch/s390/include/asm/fpu/types.h b/arch/s390/include/asm/fpu/types.h
index d889e9436865..b1afa13c07b7 100644
--- a/arch/s390/include/asm/fpu/types.h
+++ b/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 */
diff --git a/arch/s390/kernel/sysinfo.c b/arch/s390/kernel/sysinfo.c
index f6f8f498c9be..b439f17516eb 100644
--- a/arch/s390/kernel/sysinfo.c
+++ b/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)
diff --git a/lib/raid6/s390vx.uc b/lib/raid6/s390vx.uc
index cd0b9e95f499..7b0b355e1a26 100644
--- a/lib/raid6/s390vx.uc
+++ b/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;
 
-- 
2.40.1