[PATCH 6.9 357/374] powerpc/uaccess: Use YZ asm constraint for ld

Greg Kroah-Hartman
2024-06-06T14:11:24Z

From: Michael Ellerman <mpe@ellerman.id.au>

[ 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@ellerman.id.au>
Link: https://msgid.link/20240529123029.146953-2-mpe@ellerman.id.au
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/include/asm/uaccess.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index de10437fd2065..ac4f6e4ae5810 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -165,8 +165,19 @@ do { \
#endif

#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_goto_output( \
--
2.43.0