linux-kernel - Re: [PATCH] x86: Fix earlyprintk ttyS2/3

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Date:	Tue, 07 Apr 2015 23:00:38 +0800
From:	Daniel J Blueman <daniel@...ascale.com>
To:	Joe Perches <joe@...ches.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Steffen Persvold <sp@...ascale.com>
Subject: Re: [PATCH] x86: Fix earlyprintk ttyS2/3

On Tue, Apr 7, 2015 at 10:39 PM, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2015-04-07 at 22:29 +0800, Daniel J Blueman wrote:
>>  Quite a few platforms use ttyS2 for their serial-over-LAN, so fix 
>> early
>>  printk support for ttyS2 and 3, avoiding the need to hard-code the 
>> IO port.
> []
>>  diff --git a/arch/x86/boot/early_serial_console.c 
>> b/arch/x86/boot/early_serial_console.c
> []
>>  @@ -71,15 +71,16 @@ static void parse_earlyprintk(void)
>>   			else
>>   				pos = e - arg;
>>   		} else if (!strncmp(arg + pos, "ttyS", 4)) {
>>  -			static const int bases[] = { 0x3f8, 0x2f8 };
>>  -			int idx = 0;
>>  +			static const int bases[] = {0x3f8, 0x2f8, 0x3e8, 0x2e8};
>>  +			unsigned idx = 0;
>> 
>>   			if (!strncmp(arg + pos, "ttyS", 4))
>>   				pos += 4;
>> 
>>  -			if (arg[pos++] == '1')
>>  -				idx = 1;
>>  +			if ((arg[pos] - '0') < (sizeof(bases) / sizeof(bases[0])))
>>  +				idx = arg[pos] - '0';
> 
> This doesn't prevent negative indexing in case someone
> does something like shift key typo "ttyS!" for "ttyS1".
> 
> I've done that.

Gah; late night coding syndrome. Adding the missing cast in the first 
case only:

Subject: [PATCH v2] x86: Fix earlyprintk ttyS2/3

Quite a few platforms use ttyS2 for their serial-over-LAN, so fix early
printk support for ttyS2 and 3, avoiding the need to hard-code the IO 
port.

v2: Add missing unsigned cast to correct range check

Signed-off-by: Daniel J Blueman <daniel@...ascale.com>
---
 arch/x86/boot/early_serial_console.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/early_serial_console.c 
b/arch/x86/boot/early_serial_console.c
index 5df2869..3d7f112 100644
--- a/arch/x86/boot/early_serial_console.c
+++ b/arch/x86/boot/early_serial_console.c
@@ -71,15 +71,16 @@ static void parse_earlyprintk(void)
 			else
 				pos = e - arg;
 		} else if (!strncmp(arg + pos, "ttyS", 4)) {
-			static const int bases[] = { 0x3f8, 0x2f8 };
+			static const int bases[] = {0x3f8, 0x2f8, 0x3e8, 0x2e8};
 			int idx = 0;

 			if (!strncmp(arg + pos, "ttyS", 4))
 				pos += 4;

-			if (arg[pos++] == '1')
-				idx = 1;
+			if ((unsigned)(arg[pos] - '0') < (sizeof(bases) / sizeof(bases[0])))
+				idx = arg[pos] - '0';

+			pos++;
 			port = bases[idx];
 		}

-- 

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