linux-kernel - Re: [PATCH] firmware: dmi_scan: Fix ordering of product

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Date:	Thu, 16 Apr 2015 14:22:45 +0800
From:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:	Jean Delvare <jdelvare@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Ben Hutchings <ben@...adent.org.uk>,
	Artem Savkov <artem.savkov@...il.com>,
	Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH] firmware: dmi_scan: Fix ordering of product_uuid

On 2015/4/15 17:02, Jean Delvare wrote:
> In function dmi_present(), dmi_walk_early() calls dmi_table(), which
> calls dmi_decode(), which ultimately calls dmi_save_uuid(). This last
> function makes a decision based on the value of global variable
> dmi_ver. The problem is that this variable is set right _after_
> dmi_walk_early() returns. So dmi_save_uuid() always sees dmi_ver == 0
> regardless of the actual version implemented.
>
> This causes /sys/class/dmi/id/product_uuid to always use the old
> ordering even on systems implementing DMI/SMBIOS 2.6 or later, which
> should use the new ordering.
>
> This is broken since kernel v3.8 for legacy DMI implementations and
> since kernel v3.10 for SMBIOS 2 implementations. SMBIOS 3
> implementations with the 64-bit entry point are not affected.
>
> The first breakage does not matter much as in practice legacy DMI
> implementations are always for versions older than 2.6, which is when
> the UUID ordering changed. The second breakage is more problematic as
> it affects the vast majority of x86 systems manufactured since 2009.
>
> Signed-off-by: Jean Delvare <jdelvare@...e.de>
> Fixes: 9f9c9cbb6057 ("drivers/firmware/dmi_scan.c: fetch dmi version from SMBIOS if it exists")
I think above line should be removed as dmi_ver is set before 
dmi_walk_early with the commit, see below clip.
We did get right UUID order with SMBIOS 2.6 per customer test.

+static int __init smbios_present(const char __iomem *p)
+{
+    u8 buf[32];
+    int offset = 0;
+
+    memcpy_fromio(buf, p, 32);
+    if ((buf[5] < 32) && dmi_checksum(buf, buf[5])) {
+        dmi_ver = (buf[6] << 8) + buf[7];
> Fixes: 79bae42d51a5 ("dmi_scan: refactor dmi_scan_machine(), {smbios,dmi}_present()")
> Cc: Zhenzhong Duan <zhenzhong.duan@...cle.com>
> Cc: Ben Hutchings <ben@...adent.org.uk>
> Cc: Artem Savkov <artem.savkov@...il.com>
> Cc: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
> Cc: Matt Fleming <matt.fleming@...el.com>
> Cc: stable@...r.kernel.org [v3.10+]
> ---
>   drivers/firmware/dmi_scan.c |    7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> --- linux-4.0.orig/drivers/firmware/dmi_scan.c	2015-04-13 00:12:50.000000000 +0200
> +++ linux-4.0/drivers/firmware/dmi_scan.c	2015-04-15 10:24:37.556994240 +0200
> @@ -499,18 +499,19 @@ static int __init dmi_present(const u8 *
>   	buf += 16;
>   
>   	if (memcmp(buf, "_DMI_", 5) == 0 && dmi_checksum(buf, 15)) {
> +		if (smbios_ver)
> +			dmi_ver = smbios_ver;
> +		else
> +			dmi_ver = (buf[14] & 0xF0) << 4 | (buf[14] & 0x0F);
>   		dmi_num = get_unaligned_le16(buf + 12);
>   		dmi_len = get_unaligned_le16(buf + 6);
>   		dmi_base = get_unaligned_le32(buf + 8);
>   
>   		if (dmi_walk_early(dmi_decode) == 0) {
>   			if (smbios_ver) {
> -				dmi_ver = smbios_ver;
>   				pr_info("SMBIOS %d.%d present.\n",
>   				       dmi_ver >> 8, dmi_ver & 0xFF);
>   			} else {
> -				dmi_ver = (buf[14] & 0xF0) << 4 |
> -					   (buf[14] & 0x0F);
>   				pr_info("Legacy DMI %d.%d present.\n",
>   				       dmi_ver >> 8, dmi_ver & 0xFF);
>   			}
>
>
The basic idea is right, but you ignore the case dmi_walk_early may 
fail, though looks impossible when bootup.

Better to add below for robust.

@@ -521,6 +521,6 @@ static int __init dmi_present(const u8 *

              return 0;
          }
      }
+    dmi_ver = 0;
      return 1;
  }

zduan
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