linux-kernel - [PATCH] ARCv2: save ABI registers across signal handling

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Date:   Wed,  9 Jun 2021 13:38:36 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, libc-alpha@...rceware.org,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        stable@...r.kernel.org,
        Vladimir Isaev <Vladimir.Isaev@...opsys.com>
Subject: [PATCH] ARCv2: save ABI registers across signal handling

ARCv2 has some configuration dependent registers (r30, r58, r59) which
could be targetted by the compiler. To keep the ABI stable, these were
unconditionally part of the glibc ABI
(sysdeps/unix/sysv/linux/arc/sys/ucontext.h:mcontext_t) however we
missed populating them (by saving/restoring them across signal
handling).

This patch fixes the issue by
 - adding arcv2 ABI regs to kernel struct sigcontext
 - populating them during signal handling

Change to struct sigcontext might seem like a glibc ABI change (although
it primarily uses ucontext_t:mcontext_t) but the fact is
 - it has only been extended (existing fields are not touched)
 - the old sigcontext was ABI incomplete to begin with anyways

Fixes: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/53
Cc: <stable@...r.kernel.org>
Reported-by: Vladimir Isaev <isaev@...opsys.com>
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/include/uapi/asm/sigcontext.h |  1 +
 arch/arc/kernel/signal.c               | 29 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/arc/include/uapi/asm/sigcontext.h b/arch/arc/include/uapi/asm/sigcontext.h
index 95f8a4380e11..7a5449dfcb29 100644
--- a/arch/arc/include/uapi/asm/sigcontext.h
+++ b/arch/arc/include/uapi/asm/sigcontext.h
@@ -18,6 +18,7 @@
  */
 struct sigcontext {
 	struct user_regs_struct regs;
+	struct user_regs_arcv2 v2abi;
 };
 
 #endif /* _ASM_ARC_SIGCONTEXT_H */
diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
index b3ccb9e5ffe4..534b3d9bafc8 100644
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -94,6 +94,21 @@ stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
 
 	err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
 			     sizeof(sf->uc.uc_mcontext.regs.scratch));
+
+	if (is_isa_arcv2()) {
+		struct user_regs_arcv2 v2abi;
+
+		v2abi.r30 = regs->r30;
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+		v2abi.r58 = regs->r58;
+		v2abi.r59 = regs->r59;
+#else
+		v2abi.r58 = v2abi.r59 = 0;
+#endif
+		err |= __copy_to_user(&(sf->uc.uc_mcontext.v2abi), &v2abi,
+				      sizeof(sf->uc.uc_mcontext.v2abi));
+	}
+
 	err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 
 	return err ? -EFAULT : 0;
@@ -109,6 +124,20 @@ static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 	err |= __copy_from_user(&uregs.scratch,
 				&(sf->uc.uc_mcontext.regs.scratch),
 				sizeof(sf->uc.uc_mcontext.regs.scratch));
+
+	if (is_isa_arcv2()) {
+		struct user_regs_arcv2 v2abi;
+
+		err |= __copy_from_user(&v2abi,	&(sf->uc.uc_mcontext.v2abi),
+					sizeof(sf->uc.uc_mcontext.v2abi));
+
+		regs->r30 = v2abi.r30;
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+		regs->r58 = v2abi.r58;
+		regs->r59 = v2abi.r59;
+#endif
+	}
+
 	if (err)
 		return -EFAULT;
 
-- 
2.25.1