linux-kernel - [RFC PATCH v1 5/5] s390/unwind_user: Enable signal frame unwinding of user space

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Message-ID: <20260127153331.2902504-6-jremus@linux.ibm.com>
Date: Tue, 27 Jan 2026 16:33:31 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
        "Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
        Dylan Hatch <dylanbhatch@...gle.com>
Subject: [RFC PATCH v1 5/5] s390/unwind_user: Enable signal frame unwinding of user space

Provide a s390-specific implementation of unwind_user_signal_next(),
that unwinds from a (RT) signal frame.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
 arch/s390/include/asm/unwind_user.h | 57 +++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/arch/s390/include/asm/unwind_user.h b/arch/s390/include/asm/unwind_user.h
index a7b97ea01c26..8f5524a24ae1 100644
--- a/arch/s390/include/asm/unwind_user.h
+++ b/arch/s390/include/asm/unwind_user.h
@@ -7,6 +7,7 @@
 #include <linux/types.h>
 #include <asm/asm-offsets.h>
 #include <asm/fpu.h>
+#include <asm/sigframe.h>
 #include <asm/stacktrace.h>
 #include <linux/unwind_user_types.h>
 
@@ -67,6 +68,62 @@ static inline int arch_unwind_user_get_reg(unsigned long *val,
 }
 #define unwind_user_get_reg arch_unwind_user_get_reg
 
+#define SVC_OPCODE		0x0a
+#define INSN_SVC_SIGRETURN	((SVC_OPCODE << 8) | __NR_sigreturn)
+#define INSN_SVC_RT_SIGRETURN	((SVC_OPCODE << 8) | __NR_rt_sigreturn)
+
+static inline int unwind_user_signal_next(struct unwind_user_state *state)
+{
+	unsigned short insn;
+	const _sigregs __user *sr;
+	unsigned long sp, fp, ra;
+
+	/* ABI requires IP to be 2-byte aligned. */
+	if (state->ip & 1)
+		return -EINVAL;
+
+	if (__get_user(insn, (unsigned short __user *)state->ip))
+		return -EINVAL;
+
+	/*
+	 * A signal frame has the instruction pointer pointing to
+	 * svc $__NR_sigreturn or svc $__NR_rt_sigreturn
+	 */
+	switch (insn) {
+	case INSN_SVC_SIGRETURN:
+		/* New-style non-RT frame.  */
+		const struct sigframe __user *sf;
+
+		sf = (struct sigframe __user *)state->sp;
+		if (__get_user(sr, (_sigregs __user **)&sf->sc.sregs))
+			return -EINVAL;
+		break;
+	case INSN_SVC_RT_SIGRETURN:
+		/* New-style RT frame.  */
+		const struct rt_sigframe __user *rt_sf;
+
+		rt_sf = (struct rt_sigframe __user *)state->sp;
+		sr = (_sigregs __user *)&rt_sf->uc.uc_mcontext;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (__get_user(sp, (unsigned long __user *)&sr->regs.gprs[15]))
+		return -EINVAL;
+	if (__get_user(fp, (unsigned long __user *)&sr->regs.gprs[11]))
+		return -EINVAL;
+	if (__get_user(ra, (unsigned long __user *)&sr->regs.psw.addr))
+		return -EINVAL;
+
+	state->ip = ra;
+	state->sp = sp;
+	state->fp = fp;
+	state->topmost = false;
+	return 0;
+}
+#define unwind_user_signal_next unwind_user_signal_next
+
 #endif /* CONFIG_UNWIND_USER */
 
 #ifdef CONFIG_HAVE_UNWIND_USER_FP
-- 
2.51.0