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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Sven Schnelle <svens@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>
Subject: [PATCH 5.12 231/242] s390/vdso64: add sigreturn,rt_sigreturn and restart_syscall
Date:   Thu, 15 Jul 2021 20:39:53 +0200
Message-Id: <20210715182633.531536608@linuxfoundation.org>
In-Reply-To: <20210715182551.731989182@linuxfoundation.org>
References: <20210715182551.731989182@linuxfoundation.org>
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From: Sven Schnelle <svens@linux.ibm.com>

commit 686341f2548b5a4c4ab1ee22427e046027ae1c9c upstream.

Add minimalistic trampolines to vdso64 so we can return from signal
without using the stack which requires pgm check handler hacks when
NX is enabled.

restart_syscall will be called from vdso to work around the architectural
limitation that the syscall number might be encoded in the svc instruction,
and therefore can not be changed.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/kernel/vdso64/vdso64.lds.S        |    3 +++
 arch/s390/kernel/vdso64/vdso_user_wrapper.S |   17 +++++++++++++++++
 2 files changed, 20 insertions(+)

--- a/arch/s390/kernel/vdso64/vdso64.lds.S
+++ b/arch/s390/kernel/vdso64/vdso64.lds.S
@@ -137,6 +137,9 @@ VERSION
 		__kernel_clock_gettime;
 		__kernel_clock_getres;
 		__kernel_getcpu;
+		__kernel_restart_syscall;
+		__kernel_rt_sigreturn;
+		__kernel_sigreturn;
 	local: *;
 	};
 }
--- a/arch/s390/kernel/vdso64/vdso_user_wrapper.S
+++ b/arch/s390/kernel/vdso64/vdso_user_wrapper.S
@@ -37,3 +37,20 @@ vdso_func gettimeofday
 vdso_func clock_getres
 vdso_func clock_gettime
 vdso_func getcpu
+
+.macro vdso_syscall func,syscall
+	.globl __kernel_\func
+	.type  __kernel_\func,@function
+	.align 8
+__kernel_\func:
+	CFI_STARTPROC
+	svc	\syscall
+	/* Make sure we notice when a syscall returns, which shouldn't happen */
+	.word	0
+	CFI_ENDPROC
+	.size	__kernel_\func,.-__kernel_\func
+.endm
+
+vdso_syscall restart_syscall,__NR_restart_syscall
+vdso_syscall sigreturn,__NR_sigreturn
+vdso_syscall rt_sigreturn,__NR_rt_sigreturn