This is a note to let you know that I've just added the patch titled
powerpc/uaccess: Use YZ asm constraint for ld
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-uaccess-use-yz-asm-constraint-for-ld.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 77c8c18109f7d833e8b3c948d29eea1b258898c0
Author: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Date: Wed May 29 22:30:29 2024 +1000
powerpc/uaccess: Use YZ asm constraint for ld
[ Upstream commit 50934945d54238d2d6d8db4b7c1d4c90d2696c57 ]
The 'ld' instruction requires a 4-byte aligned displacement because it
is a DS-form instruction. But the "m" asm constraint doesn't enforce
that.
Add a special case of __get_user_asm2_goto() so that the "YZ" constraint
can be used for "ld".
The "Z" constraint is documented in the GCC manual PowerPC machine
constraints, and specifies a "memory operand accessed with indexed or
indirect addressing". "Y" is not documented in the manual but specifies
a "memory operand for a DS-form instruction". Using both allows the
compiler to generate a DS-form "ld" or X-form "ldx" as appropriate.
The change has to be conditional on CONFIG_PPC_KERNEL_PREFIXED because
the "Y" constraint does not guarantee 4-byte alignment when prefixed
instructions are enabled.
No build errors have been reported due to this, but the possibility is
there depending on compiler code generation decisions.
Fixes: c20beffeec3c ("powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()")
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20240529123029.146953-2-mpe@xxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index b2680070d65d6..a1fddbd843f00 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -151,8 +151,19 @@ do { \
: label)
#ifdef __powerpc64__
+#ifdef CONFIG_PPC_KERNEL_PREFIXED
#define __get_user_asm2_goto(x, addr, label) \
__get_user_asm_goto(x, addr, label, "ld")
+#else
+#define __get_user_asm2_goto(x, addr, label) \
+ asm_goto_output( \
+ "1: ld%U1%X1 %0, %1 # get_user\n" \
+ EX_TABLE(1b, %l2) \
+ : "=r" (x) \
+ : DS_FORM_CONSTRAINT (*addr) \
+ : \
+ : label)
+#endif // CONFIG_PPC_KERNEL_PREFIXED
#else /* __powerpc64__ */
#define __get_user_asm2_goto(x, addr, label) \
asm_volatile_goto( \
