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From: Ben Hutchings <ben@decadent.org.uk>
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Date: Thu, 30 Apr 2020 13:31:32 +0100
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Subject: [klibc] alpha: Set sa_restorer for signals and disable executable stack
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Origin: https://git.kernel.org/pub/scm/libs/klibc/klibc.git/commit?id=7f84d11885cf3e9298d53a2714800a8ac9c4dd74
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Date: Sun, 23 Aug 2020 15:18:19 +0100
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Subject: [klibc] alpha: Pass restorer to rt_sigaction() and disable executable stack
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Add a __sigreturn routine and point sa_restorer to it by default, so
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that the kernel doesn't create stack trampolines for signal return.
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With that done, we no longer need an executable stack.
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alpha does not support the SA_RESTORER flag, but allows specifiying a
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restorer callback as an additional parameter to rt_sigaction().
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Define an __rt_sigreturn routine and pass that, so that the kernel
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doesn't create stack trampolines for signal return. With that done,
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we no longer need an executable stack.
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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usr/include/arch/alpha/klibc/archconfig.h | 3 +++
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usr/include/arch/alpha/klibc/archsignal.h | 8 +++++++-
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usr/klibc/arch/alpha/Kbuild | 2 +-
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usr/klibc/arch/alpha/MCONFIG | 5 ++---
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usr/klibc/arch/alpha/sigreturn.S | 16 ++++++++++++++++
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4 files changed, 22 insertions(+), 4 deletions(-)
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create mode 100644 usr/klibc/arch/alpha/sigreturn.S
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usr/klibc/arch/alpha/rt_sigreturn.S | 18 ++++++++++++++++++
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usr/klibc/sigaction.c | 2 +-
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5 files changed, 29 insertions(+), 6 deletions(-)
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create mode 100644 usr/klibc/arch/alpha/rt_sigreturn.S
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diff --git a/usr/include/arch/alpha/klibc/archconfig.h b/usr/include/arch/alpha/klibc/archconfig.h
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index 272fee0a..b80d299f 100644
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--- a/usr/include/arch/alpha/klibc/archconfig.h
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+++ b/usr/include/arch/alpha/klibc/archconfig.h
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@@ -12,4 +12,7 @@
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#define _KLIBC_USE_RT_SIG 1
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#define _KLIBC_STATFS_F_TYPE_64 0
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diff --git a/usr/include/arch/alpha/klibc/archsignal.h b/usr/include/arch/alpha/klibc/archsignal.h
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index 2193a352..0906f338 100644
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--- a/usr/include/arch/alpha/klibc/archsignal.h
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+++ b/usr/include/arch/alpha/klibc/archsignal.h
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@@ -9,6 +9,12 @@
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#define _KLIBC_ARCHSIGNAL_H
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+/* So that we can avoid stack trampolines */
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+#define _KLIBC_NEEDS_SA_RESTORER 1
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#include <asm/signal.h>
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-/* No special stuff for this architecture */
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+
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#endif /* _KLIBC_ARCHCONFIG_H */
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+/*
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+ * Passed as last parameter to __rt_sigaction(). It is a function
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+ * that should have type void (void), but syscalls.pl can't parse
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+ * function types in syscall parameters.
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+ */
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+extern void __rt_sigreturn;
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#endif
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diff --git a/usr/klibc/arch/alpha/Kbuild b/usr/klibc/arch/alpha/Kbuild
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index 2e566eb6..eef7cfb4 100644
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index 2e566eb6..6a62d47d 100644
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--- a/usr/klibc/arch/alpha/Kbuild
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+++ b/usr/klibc/arch/alpha/Kbuild
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@@ -9,7 +9,7 @@
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always := crt0.o
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targets := crt0.o
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-klib-y := pipe.o setjmp.o syscall.o sysdual.o
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+klib-y := pipe.o setjmp.o syscall.o sysdual.o sigreturn.o
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+klib-y := pipe.o setjmp.o syscall.o sysdual.o rt_sigreturn.o
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# Special CFLAGS for the divide code
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DIVCFLAGS = $(KLIBCREQFLAGS) $(KLIBCARCHREQFLAGS) \
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-KLIBCEXECSTACK := y
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+# Kernel uses our sa_restorer for signal return
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+KLIBCEXECSTACK := n
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diff --git a/usr/klibc/arch/alpha/sigreturn.S b/usr/klibc/arch/alpha/sigreturn.S
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diff --git a/usr/klibc/arch/alpha/rt_sigreturn.S b/usr/klibc/arch/alpha/rt_sigreturn.S
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new file mode 100644
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index 00000000..95415edd
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index 00000000..e41b5544
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--- /dev/null
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+++ b/usr/klibc/arch/alpha/sigreturn.S
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@@ -0,0 +1,16 @@
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+++ b/usr/klibc/arch/alpha/rt_sigreturn.S
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@@ -0,0 +1,18 @@
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+/*
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+ * arch/alpha/sigreturn.S
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+ */
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+
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+#include <machine/asm.h>
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+#include <asm/unistd.h>
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+
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+ .text
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+ .align 3
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+ .type __sigreturn,@function
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+ .ent __sigreturn,0
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+ .globl __sigreturn
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+__sigreturn:
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+ mov sp,a0 ; struct sigcontext on stack
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+ lda v0,__NR_sigreturn(zero)
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+ .type __rt_sigreturn,@function
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+ .ent __rt_sigreturn,0
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+ .globl __rt_sigreturn
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+__rt_sigreturn:
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+ mov sp,a0 # struct sigcontext on stack
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+ lda v0,__NR_rt_sigreturn(zero)
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+ callsys
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+ .size __sigreturn,.-__sigreturn
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+ .size __rt_sigreturn,.-__rt_sigreturn
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+ .end __rt_sigreturn
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diff --git a/usr/klibc/sigaction.c b/usr/klibc/sigaction.c
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index 19a8a54b..108c8385 100644
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--- a/usr/klibc/sigaction.c
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+++ b/usr/klibc/sigaction.c
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@@ -47,7 +47,7 @@ int sigaction(int sig, const struct sigaction *act, struct sigaction *oact)
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rv = __rt_sigaction(sig, act, oact, restorer, sizeof(sigset_t));
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}
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# elif defined(__alpha__)
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- rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t), NULL);
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+ rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t), &__rt_sigreturn);
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# else
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rv = __rt_sigaction(sig, act, oact, sizeof(sigset_t));
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# endif
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