klibc - Aug 2020 - [klibc:execstack-fixes] alpha: Set sa_restorer for signals and disable executable stack

Commit-ID:  7f84d11885cf3e9298d53a2714800a8ac9c4dd74
Gitweb:    
http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=7f84d11885cf3e9298d53a2714800a8ac9c4dd74
Author:     Ben Hutchings <ben at decadent.org.uk>
AuthorDate: Thu, 30 Apr 2020 13:31:32 +0100
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Thu, 20 Aug 2020 23:22:58 +0100

[klibc] alpha: Set sa_restorer for signals and disable executable stack

Add a __sigreturn routine and point sa_restorer to it by default, so
that the kernel doesn't create stack trampolines for signal return.
With that done, we no longer need an executable stack.

Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 usr/include/arch/alpha/klibc/archconfig.h |  3 +++
 usr/klibc/arch/alpha/Kbuild               |  2 +-
 usr/klibc/arch/alpha/MCONFIG              |  5 ++---
 usr/klibc/arch/alpha/sigreturn.S          | 16 ++++++++++++++++
 4 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/usr/include/arch/alpha/klibc/archconfig.h
b/usr/include/arch/alpha/klibc/archconfig.h
index 272fee0a..b80d299f 100644
--- a/usr/include/arch/alpha/klibc/archconfig.h
+++ b/usr/include/arch/alpha/klibc/archconfig.h
@@ -12,4 +12,7 @@
 #define _KLIBC_USE_RT_SIG 1
 #define _KLIBC_STATFS_F_TYPE_64 0
 
+/* So that we can avoid stack trampolines */
+#define _KLIBC_NEEDS_SA_RESTORER 1
+
 #endif				/* _KLIBC_ARCHCONFIG_H */
diff --git a/usr/klibc/arch/alpha/Kbuild b/usr/klibc/arch/alpha/Kbuild
index 2e566eb6..eef7cfb4 100644
--- a/usr/klibc/arch/alpha/Kbuild
+++ b/usr/klibc/arch/alpha/Kbuild
@@ -9,7 +9,7 @@
 
 always  := crt0.o
 targets := crt0.o
-klib-y := pipe.o setjmp.o syscall.o sysdual.o
+klib-y := pipe.o setjmp.o syscall.o sysdual.o sigreturn.o
 
 # Special CFLAGS for the divide code
 DIVCFLAGS = $(KLIBCREQFLAGS) $(KLIBCARCHREQFLAGS) \
diff --git a/usr/klibc/arch/alpha/MCONFIG b/usr/klibc/arch/alpha/MCONFIG
index 072adb85..e71db264 100644
--- a/usr/klibc/arch/alpha/MCONFIG
+++ b/usr/klibc/arch/alpha/MCONFIG
@@ -15,6 +15,5 @@ KLIBCBITSIZE  = 64
 # the binary.
 KLIBCSHAREDFLAGS	= -Ttext-segment 0x1c0000000
 
-# Kernel uses stack trampoline for signal return unless we set
-# sa_restorer
-KLIBCEXECSTACK := y
+# Kernel uses our sa_restorer for signal return
+KLIBCEXECSTACK := n
diff --git a/usr/klibc/arch/alpha/sigreturn.S b/usr/klibc/arch/alpha/sigreturn.S
new file mode 100644
index 00000000..95415edd
--- /dev/null
+++ b/usr/klibc/arch/alpha/sigreturn.S
@@ -0,0 +1,16 @@
+/*
+ * arch/alpha/sigreturn.S
+ */
+
+#include <asm/unistd.h>
+
+	.text
+	.align	3
+	.type	__sigreturn, at function
+	.ent	__sigreturn,0
+	.globl	__sigreturn
+__sigreturn:
+	mov	sp,a0			; struct sigcontext on stack
+	lda	v0,__NR_sigreturn(zero)
+	callsys
+	.size	__sigreturn,.-__sigreturn