Re: AMD Geode NOPL emulation for kernel 2.6.36-rc2

["H. Peter Anvin" <hpa@zytor.com>]

You actually have to check the get_user return, or use exception brackets....

"Matteo Croce" <matteo@openwrt.org> wrote:

>On Fri, Aug 27, 2010 at 8:48 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> You're doing user-space references without get_user().
>>
>>        -hpa
>>
>> --
>> H. Peter Anvin, Intel Open Source Technology Center
>> I work for Intel.  I don't speak on their behalf.
>>
>>
>
>Here with get_user.
>I CC Natale which is my beta tester, he have some Alix boards running 24/24
>with my patch
>
>--- a/arch/x86/kernel/Makefile	2010-08-27 19:42:01.795858001 +0200
>+++ b/arch/x86/kernel/Makefile	2010-08-27 19:42:12.525858001 +0200
>@@ -88,6 +88,8 @@
> obj-$(CONFIG_APB_TIMER)		+= apb_timer.o
>
> obj-$(CONFIG_K8_NB)		+= k8.o
>+obj-$(CONFIG_GEODE_NOPL)	+= nopl_emu.o
>+obj-$(CONFIG_GEODE_NOPL)	+= nopl_emu.o
> obj-$(CONFIG_DEBUG_RODATA_TEST)	+= test_rodata.o
> obj-$(CONFIG_DEBUG_NX_TEST)	+= test_nx.o
>
>--- a/arch/x86/kernel/cpu/amd.c	2010-08-27 19:42:01.855858001 +0200
>+++ b/arch/x86/kernel/cpu/amd.c	2010-08-27 19:42:12.535858001 +0200
>@@ -137,11 +137,15 @@
> 		return;
> 	}
>
>+#ifdef CONFIG_GEODE_NOPL
> 	if (c->x86_model == 10) {
>-		/* AMD Geode LX is model 10 */
>-		/* placeholder for any needed mods */
>+		/* Geode only lacks the NOPL instruction to be i686,
>+		   but we can promote it to a i686 class cpu
>+		   and emulate NOPLs in the exception handler*/
>+		boot_cpu_data.x86 = 6;
> 		return;
> 	}
>+#endif
> }
>
> static void __cpuinit amd_k7_smp_check(struct cpuinfo_x86 *c)
>--- a/arch/x86/kernel/entry_32.S	2010-08-27 19:42:01.735858001 +0200
>+++ b/arch/x86/kernel/entry_32.S	2010-08-27 19:42:12.535858001 +0200
>@@ -978,7 +978,11 @@
> 	RING0_INT_FRAME
> 	pushl $0
> 	CFI_ADJUST_CFA_OFFSET 4
>+#ifdef CONFIG_GEODE_NOPL
>+	pushl $do_nopl_emu
>+#else
> 	pushl $do_invalid_op
>+#endif
> 	CFI_ADJUST_CFA_OFFSET 4
> 	jmp error_code
> 	CFI_ENDPROC
>--- /dev/null	1970-01-01 00:00:00.000000000 +0000
>+++ b/arch/x86/kernel/nopl_emu.c	2010-08-27 22:09:58.005858001 +0200
>@@ -0,0 +1,124 @@
>+/*
>+ *  linux/arch/x86/kernel/nopl_emu.c
>+ *
>+ *  Copyright (C) 2002  Willy Tarreau
>+ *  Copyright (C) 2010  Matteo Croce
>+ */
>+
>+#include <asm/processor.h>
>+#include <asm/traps.h>
>+#include <asm/uaccess.h>
>+
>+/* This code can be used to allow the AMD Geode to hopefully correctly execute
>+ * some code which was originally compiled for an i686, by emulating NOPL,
>+ * the only missing i686 instruction in the CPU
>+ *
>+ * Willy Tarreau <willy@meta-x.org>
>+ * Matteo Croce <technoboy85@gmail.com>
>+ */
>+
>+static inline int do_1f(u8 *ip)
>+{
>+	u8 val1, val2;
>+	int length = 3;
>+	get_user(val1, ip);
>+	switch (val1) {
>+	case 0x84:
>+		get_user(val1, ip + 5);
>+		if (!val1)
>+			length++;
>+		else
>+			return 0;
>+	case 0x80:
>+		get_user(val1, ip + 4);
>+		get_user(val2, ip + 3);
>+		if (!val1 && !val2)
>+			length += 2;
>+		else
>+			return 0;
>+	case 0x44:
>+		get_user(val1, ip + 2);
>+		if (!val1)
>+			length++;
>+		else
>+			return 0;
>+	case 0x40:
>+		get_user(val1, ip + 1);
>+		if (!val1)
>+			length++;
>+		else
>+			return 0;
>+	case 0x00:
>+		return length;
>+	}
>+	return 0;
>+}
>+
>+static inline int do_0f(u8 *ip)
>+{
>+	u8 val;
>+	get_user(val, ip);
>+	if (val == 0x1f)
>+		return do_1f(ip + 1);
>+	return 0;
>+}
>+
>+static inline int do_66(u8 *ip)
>+{
>+	u8 val;
>+	get_user(val, ip);
>+	if (val == 0x90)
>+		return 2;
>+	if (val == 0x0f) {
>+		int res = do_0f(ip + 1);
>+		if (res)
>+			return res + 1;
>+		else
>+			return 0;
>+	}
>+	return 0;
>+}
>+
>+static inline int do_start(u8 *ip)
>+{
>+	u8 val;
>+	get_user(val, ip);
>+	if (val == 0x0f)
>+		return do_0f(ip + 1);
>+	if (val == 0x66)
>+		return do_66(ip + 1);
>+	return 0;
>+}
>+
>+/* [do_nopl_emu] is called by exception 6 after an invalid opcode has been
>+ * encountered. It will try to emulate it by doing nothing,
>+ * and will send a SIGILL or SIGSEGV to the process if not possible.
>+ * the NOPL can have variable length opcodes:
>+
>+bytes number	opcode
>+	2	66 90
>+	3	0f 1f 00
>+	4	0f 1f 40 00
>+	5	0f 1f 44 00 00
>+	6	66 0f 1f 44 00 00
>+	7	0f 1f 80 00 00 00 00
>+	8	0f 1f 84 00 00 00 00 00
>+	9	66 0f 1f 84 00 00 00 00 00
>+*/
>+void do_nopl_emu(struct pt_regs *regs, long error_code)
>+{
>+	u8 *ip = (u8 *)instruction_pointer(regs);
>+	int res = do_start(ip);
>+
>+	if (res) {
>+		int i = 0;
>+		do {
>+			ip += res;
>+			i++;
>+			res = do_start(ip);
>+		} while(res);
>+		printk(KERN_DEBUG "geode_nopl: emulated %d instructions\n", i);
>+		regs->ip = (typeof(regs->ip))ip;
>+	} else
>+		do_invalid_op(regs, error_code);
>+}
>
>
>-- 
>Matteo Croce
>OpenWrt developer
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