linux-kernel - [PATCH 07/18] arm: propagate the calling convention changes down to csum_partial_copy_from

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Message-Id: <20200721202549.4150745-7-viro@ZenIV.linux.org.uk>
Date:   Tue, 21 Jul 2020 21:25:38 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: [PATCH 07/18] arm: propagate the calling convention changes down to csum_partial_copy_from_user()

From: Al Viro <viro@...iv.linux.org.uk>

... and get rid of the "clean the destination on error" crap.
Simplifies the fault handlers and the function itself...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 arch/arm/include/asm/checksum.h       |  7 ++-----
 arch/arm/lib/csumpartialcopy.S        |  1 -
 arch/arm/lib/csumpartialcopygeneric.S |  1 +
 arch/arm/lib/csumpartialcopyuser.S    | 26 ++++++--------------------
 4 files changed, 9 insertions(+), 26 deletions(-)

diff --git a/arch/arm/include/asm/checksum.h b/arch/arm/include/asm/checksum.h
index 737db6c3c482..d434986e81b2 100644
--- a/arch/arm/include/asm/checksum.h
+++ b/arch/arm/include/asm/checksum.h
@@ -38,19 +38,16 @@ __wsum
 csum_partial_copy_nocheck(const void *src, void *dst, int len);
 
 __wsum
-csum_partial_copy_from_user(const void __user *src, void *dst, int len, __wsum sum, int *err_ptr);
+csum_partial_copy_from_user(const void __user *src, void *dst, int len);
 
 #define _HAVE_ARCH_COPY_AND_CSUM_FROM_USER
 static inline
 __wsum csum_and_copy_from_user(const void __user *src, void *dst, int len)
 {
-	int err = 0;
-
 	if (!access_ok(src, len))
 		return 0;
 
-	sum = csum_partial_copy_from_user(src, dst, len, ~0U, &err);
-	return err ? 0 : sum;
+	return csum_partial_copy_from_user(src, dst, len);
 }
 
 /*
diff --git a/arch/arm/lib/csumpartialcopy.S b/arch/arm/lib/csumpartialcopy.S
index aab914fbc86b..1ca6aadd649c 100644
--- a/arch/arm/lib/csumpartialcopy.S
+++ b/arch/arm/lib/csumpartialcopy.S
@@ -16,7 +16,6 @@
 
 		.macro	save_regs
 		stmfd	sp!, {r1, r4 - r8, lr}
-		mov	r3, #0
 		.endm
 
 		.macro	load_regs
diff --git a/arch/arm/lib/csumpartialcopygeneric.S b/arch/arm/lib/csumpartialcopygeneric.S
index 0b706a39a677..0fd5c10e90a7 100644
--- a/arch/arm/lib/csumpartialcopygeneric.S
+++ b/arch/arm/lib/csumpartialcopygeneric.S
@@ -86,6 +86,7 @@ sum	.req	r3
 
 FN_ENTRY
 		save_regs
+		mov	sum, #-1
 
 		cmp	len, #8			@ Ensure that we have at least
 		blo	.Lless8			@ 8 bytes to copy.
diff --git a/arch/arm/lib/csumpartialcopyuser.S b/arch/arm/lib/csumpartialcopyuser.S
index 6bd3a93eaa3c..6928781e6bee 100644
--- a/arch/arm/lib/csumpartialcopyuser.S
+++ b/arch/arm/lib/csumpartialcopyuser.S
@@ -62,9 +62,9 @@
 
 /*
  * unsigned int
- * csum_partial_copy_from_user(const char *src, char *dst, int len, int sum, int *err_ptr)
- *  r0 = src, r1 = dst, r2 = len, r3 = sum, [sp] = *err_ptr
- *  Returns : r0 = checksum, [[sp, #0], #0] = 0 or -EFAULT
+ * csum_partial_copy_from_user(const char *src, char *dst, int len)
+ *  r0 = src, r1 = dst, r2 = len
+ *  Returns : r0 = checksum or 0
  */
 
 #define FN_ENTRY	ENTRY(csum_partial_copy_from_user)
@@ -73,25 +73,11 @@
 #include "csumpartialcopygeneric.S"
 
 /*
- * FIXME: minor buglet here
- * We don't return the checksum for the data present in the buffer.  To do
- * so properly, we would have to add in whatever registers were loaded before
- * the fault, which, with the current asm above is not predictable.
+ * We report fault by returning 0 csum - impossible in normal case, since
+ * we start with 0xffffffff for initial sum.
  */
 		.pushsection .text.fixup,"ax"
 		.align	4
-9001:		mov	r4, #-EFAULT
-#ifdef CONFIG_CPU_SW_DOMAIN_PAN
-		ldr	r5, [sp, #9*4]		@ *err_ptr
-#else
-		ldr	r5, [sp, #8*4]		@ *err_ptr
-#endif
-		str	r4, [r5]
-		ldmia	sp, {r1, r2}		@ retrieve dst, len
-		add	r2, r2, r1
-		mov	r0, #0			@ zero the buffer
-9002:		teq	r2, r1
-		strbne	r0, [r1], #1
-		bne	9002b
+9001:		mov	r0, #0
 		load_regs
 		.popsection
-- 
2.11.0