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Message-Id: <20250904-memcpy_series-v2-2-9806dd1784e7@mkarcher.dialup.fu-berlin.de>
Date: Thu, 04 Sep 2025 20:53:52 +0200
From: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
To: Andreas Larsson <andreas@...sler.com>,
Babu Moger <babu.moger@...cle.com>
Cc: sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>,
John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
Anthony Yznaga <anthony.yznaga@...cle.com>,
René Rebe <rene@...ctcode.com>
Subject: [PATCH v2 2/5] sparc: fix accurate exception reporting in
copy_{from_to}_user for UltraSPARC III
Anthony Yznaga tracked down that a BUG_ON in ext4 code with large folios
enabled resulted from copy_from_user() returning impossibly large values
greater than the size to be copied. This lead to __copy_from_iter()
returning impossible values instead of the actual number of bytes it was
able to copy.
The BUG_ON has been reported in
https://lore.kernel.org/r/b14f55642207e63e907965e209f6323a0df6dcee.camel@physik.fu-berlin.de
The referenced commit introduced exception handlers on user-space memory
references in copy_from_user and copy_to_user. These handlers return from the respective function and calculate the remaining bytes left to copy
using the current register contents. The exception handlers expect that
%o2 has already been masked during the bulk copy loop, but the masking was
performed after that loop. This will fix the return value of copy_from_user
and copy_to_user in the faulting case. The behaviour of memcpy stays
unchanged.
Fixes: ee841d0aff64 ("sparc64: Convert U3copy_{from,to}_user to accurate exception reporting.")
Tested-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Reviewed-by: Anthony Yznaga <anthony.yznaga@...cle.com>
Tested-by: René Rebe <rene@...ctcode.com> # UltraSparc III+ and UltraSparc IIIi
Signed-off-by: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
---
arch/sparc/lib/U3memcpy.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/sparc/lib/U3memcpy.S b/arch/sparc/lib/U3memcpy.S
index 9248d59c734ce200f1f55e6d9913277f18715a87..bace3a18f836f1428ae0ed72b27aa1e00374089e 100644
--- a/arch/sparc/lib/U3memcpy.S
+++ b/arch/sparc/lib/U3memcpy.S
@@ -267,6 +267,7 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
faligndata %f10, %f12, %f26
EX_LD_FP(LOAD(ldd, %o1 + 0x040, %f0), U3_retl_o2)
+ and %o2, 0x3f, %o2
subcc GLOBAL_SPARE, 0x80, GLOBAL_SPARE
add %o1, 0x40, %o1
bgu,pt %XCC, 1f
@@ -336,7 +337,6 @@ FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
* Also notice how this code is careful not to perform a
* load past the end of the src buffer.
*/
- and %o2, 0x3f, %o2
andcc %o2, 0x38, %g2
be,pn %XCC, 2f
subcc %g2, 0x8, %g2
--
2.50.1
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