From 8e765da941f4f0649aca2b28234ac31adde45f06 Mon Sep 17 00:00:00 2001
From: Damian Gryski <dgryski@gmail.com>
Date: Thu, 2 Feb 2012 14:09:27 -0500
Subject: [PATCH] runtime: add runtime.cputicks() and seed fastrand with it

This patch adds a function to get the current cpu ticks.  This is
deemed to be 'sufficiently random' to use to seed fastrand to mitigate
the algorithmic complexity attacks on the hash table implementation.

On AMD64 we use the RDTSC instruction.  For 386, this instruction,
while valid, is not recognized by 8a so I've inserted the opcode by
hand.  For ARM, this routine is currently stubbed to return a constant
0 value.

Future work: update 8a to recognize RDTSC.

Fixes #2630.

R=rsc
CC=golang-dev
https://golang.org/cl/5606048
---
 src/pkg/runtime/asm_386.s   |  9 +++++++++
 src/pkg/runtime/asm_amd64.s |  7 +++++++
 src/pkg/runtime/asm_arm.s   | 10 ++++++++++
 src/pkg/runtime/proc.c      |  2 +-
 src/pkg/runtime/runtime.h   |  1 +
 5 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index 52400637be..c242af8296 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -524,6 +524,15 @@ TEXT runtime·getcallersp(SB), 7, $0
 	MOVL	sp+0(FP), AX
 	RET
 
+// int64 runtime·cputicks(void), so really
+// void runtime·cputicks(int64 *ticks)
+TEXT runtime·cputicks(SB),7,$0
+	BYTE	$0x0F; BYTE $0x31;     // RDTSC; not supported by 8a
+	MOVL	ret+0(FP), DI
+	MOVL	AX, 0(DI)
+	MOVL	DX, 4(DI)
+	RET
+
 TEXT runtime·ldt0setup(SB),7,$16
 	// set up ldt 7 to point at tls0
 	// ldt 1 would be fine on Linux, but on OS X, 7 is as low as we can go.
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index 308a66036e..9a660b5b73 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -568,4 +568,11 @@ TEXT runtime·getcallersp(SB),7,$0
 	MOVQ	sp+0(FP), AX
 	RET
 
+// int64 runtime·cputicks(void)
+TEXT runtime·cputicks(SB),7,$0
+	RDTSC
+	SHLQ	$32, DX
+	ADDQ	DX, AX
+	RET
+
 GLOBL runtime·tls0(SB), $64
diff --git a/src/pkg/runtime/asm_arm.s b/src/pkg/runtime/asm_arm.s
index 42c7677e1e..58b18626fe 100644
--- a/src/pkg/runtime/asm_arm.s
+++ b/src/pkg/runtime/asm_arm.s
@@ -265,6 +265,16 @@ TEXT runtime·getcallersp(SB),7,$-4
 TEXT runtime·emptyfunc(SB),0,$0
 	RET
 
+// int64 runtime·cputicks(), so really
+// void runtime·cputicks(int64 *ticks)
+// stubbed: return int64(0)
+TEXT runtime·cputicks(SB),7,$0
+	MOVW    0(FP), R1
+	MOVW	$0, R0
+	MOVW    R0, 0(R1)
+	MOVW    R0, 4(R1)
+	RET
+
 TEXT runtime·abort(SB),7,$-4
 	MOVW	$0, R0
 	MOVW	(R0), R1
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index cb45a0c299..5bb690aaa8 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -332,7 +332,7 @@ mcommoninit(M *m)
 	runtime·atomicstorep(&runtime·allm, m);
 
 	m->id = runtime·sched.mcount++;
-	m->fastrand = 0x49f6428aUL + m->id;
+	m->fastrand = 0x49f6428aUL + m->id + runtime·cputicks();
 	m->stackalloc = runtime·malloc(sizeof(*m->stackalloc));
 	runtime·FixAlloc_Init(m->stackalloc, FixedStack, runtime·SysAlloc, nil, nil);
 
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index df2cd149f2..692992150a 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -566,6 +566,7 @@ void	runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp);
 void	runtime·resetcpuprofiler(int32);
 void	runtime·setcpuprofilerate(void(*)(uintptr*, int32), int32);
 void	runtime·usleep(uint32);
+int64	runtime·cputicks(void);
 
 #pragma	varargck	argpos	runtime·printf	1
 #pragma	varargck	type	"d"	int32
-- 
2.50.0