From afaa6ed4b37c519afd3f593509fd490082d7b8d2 Mon Sep 17 00:00:00 2001
From: Pawel Dziepak <pdziepak@quarnos.org>
Date: Sat, 21 Sep 2013 21:52:13 +0200
Subject: [PATCH] x86[_64]: Randomize initial stack pointer on alternative
 signal stacks

If the alternate signal stack is used randomize the initial stack
pointer in the same way it is randomized on "normal" thread stacks.
Also, update MINSIGSTKSZ value so that regardless of where the new
stack pointer points to there is at least 4k of stack left.
---
 headers/posix/signal.h                   |  2 +-
 src/system/kernel/arch/x86/32/thread.cpp | 21 +++++++++++----------
 src/system/kernel/arch/x86/64/thread.cpp | 21 +++++++++++----------
 3 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/headers/posix/signal.h b/headers/posix/signal.h
index 7415cfe99c..d56cf2edfa 100644
--- a/headers/posix/signal.h
+++ b/headers/posix/signal.h
@@ -95,7 +95,7 @@ struct sigaction {
 #define SS_ONSTACK		0x1
 #define SS_DISABLE		0x2
 
-#define MINSIGSTKSZ		4096
+#define MINSIGSTKSZ		8192
 #define SIGSTKSZ		16384
 
 /* for signals using an alternate stack */
diff --git a/src/system/kernel/arch/x86/32/thread.cpp b/src/system/kernel/arch/x86/32/thread.cpp
index 66465c2951..7bed6a0f4d 100644
--- a/src/system/kernel/arch/x86/32/thread.cpp
+++ b/src/system/kernel/arch/x86/32/thread.cpp
@@ -110,6 +110,15 @@ x86_set_tls_context(Thread *thread)
 }
 
 
+static addr_t
+arch_randomize_stack_pointer(addr_t value)
+{
+	STATIC_ASSERT(MAX_RANDOM_VALUE >= B_PAGE_SIZE - 1);
+	value -= random_value() & (B_PAGE_SIZE - 1);
+	return value & ~addr_t(0xf);
+}
+
+
 static uint8*
 get_signal_stack(Thread* thread, struct iframe* frame, struct sigaction* action)
 {
@@ -119,7 +128,8 @@ get_signal_stack(Thread* thread, struct iframe* frame, struct sigaction* action)
 		&& (frame->user_sp < thread->signal_stack_base
 			|| frame->user_sp >= thread->signal_stack_base
 				+ thread->signal_stack_size)) {
-		return (uint8*)(thread->signal_stack_base + thread->signal_stack_size);
+		addr_t stackTop = thread->signal_stack_base + thread->signal_stack_size;
+		return (uint8*)arch_randomize_stack_pointer(stackTop);
 	}
 
 	return (uint8*)frame->user_sp;
@@ -202,15 +212,6 @@ arch_thread_dump_info(void *info)
 }
 
 
-static addr_t
-arch_randomize_stack_pointer(addr_t value)
-{
-	STATIC_ASSERT(MAX_RANDOM_VALUE >= B_PAGE_SIZE - 1);
-	value -= random_value() & (B_PAGE_SIZE - 1);
-	return value & ~addr_t(0xf);
-}
-
-
 /*!	Sets up initial thread context and enters user space
 */
 status_t
diff --git a/src/system/kernel/arch/x86/64/thread.cpp b/src/system/kernel/arch/x86/64/thread.cpp
index e1a337fe3c..59db5028e4 100644
--- a/src/system/kernel/arch/x86/64/thread.cpp
+++ b/src/system/kernel/arch/x86/64/thread.cpp
@@ -95,6 +95,15 @@ x86_set_tls_context(Thread* thread)
 }
 
 
+static addr_t
+arch_randomize_stack_pointer(addr_t value)
+{
+	STATIC_ASSERT(MAX_RANDOM_VALUE >= B_PAGE_SIZE - 1);
+	value -= random_value() & (B_PAGE_SIZE - 1);
+	return value & ~addr_t(0xf);
+}
+
+
 static uint8*
 get_signal_stack(Thread* thread, iframe* frame, struct sigaction* action)
 {
@@ -104,7 +113,8 @@ get_signal_stack(Thread* thread, iframe* frame, struct sigaction* action)
 			&& (frame->user_sp < thread->signal_stack_base
 				|| frame->user_sp >= thread->signal_stack_base
 					+ thread->signal_stack_size)) {
-		return (uint8*)(thread->signal_stack_base + thread->signal_stack_size);
+		addr_t stackTop = thread->signal_stack_base + thread->signal_stack_size;
+		return (uint8*)arch_randomize_stack_pointer(stackTop);
 	}
 
 	// We are going to use the stack that we are already on. We must not touch
@@ -198,15 +208,6 @@ arch_thread_dump_info(void* info)
 }
 
 
-static addr_t
-arch_randomize_stack_pointer(addr_t value)
-{
-	STATIC_ASSERT(MAX_RANDOM_VALUE >= B_PAGE_SIZE - 1);
-	value -= random_value() & (B_PAGE_SIZE - 1);
-	return value & ~addr_t(0xf);
-}
-
-
 /*!	Sets up initial thread context and enters user space
 */
 status_t