[PATCH] x86: Fix earlyprintk ttyS2/3

[PATCH] x86: Fix earlyprintk ttyS2/3

[Daniel J Blueman]

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.

Signed-off-by: Daniel J Blueman <daniel@numascale.com>
---
 arch/x86/boot/early_serial_console.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
index 5df2869..4f4c2e6 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 };
-			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';
 
+			pos++;
 			port = bases[idx];
 		}
 
-- 
2.1.0

Re: [PATCH] x86: Fix earlyprintk ttyS2/3

[Joe Perches]

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.

Re: [PATCH] x86: Fix earlyprintk ttyS2/3

[Ingo Molnar]

* Daniel J Blueman <daniel@numascale.com> 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.

Nice.

> 
> Signed-off-by: Daniel J Blueman <daniel@numascale.com>
> ---
>  arch/x86/boot/early_serial_console.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
> index 5df2869..4f4c2e6 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 };
> -			int idx = 0;
> +			static const int bases[] = {0x3f8, 0x2f8, 0x3e8, 0x2e8};
> +			unsigned idx = 0;
>  
>  			if (!strncmp(arg + pos, "ttyS", 4))
>  				pos += 4;

Btw., that's a weird pattern: why do the strncmp() twice? We already 
know that we matched, in this branch. Could be written as:

			pos += 4;

?

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

Nit: use ARRAY_SIZE()?

Not so nit: with your change, a typo in boot parameters like "ttyS-" 
would underflow the index and dereference randomly around bases[] with 
a negative index:

Also, higher indices like "ttyS4" will overflow beyond the end of the 
array.

Please add proper bounds checking and warning messages.

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

Thanks,

	Ingo

Re: [PATCH] x86: Fix earlyprintk ttyS2/3

[Daniel J Blueman]

On Tue, Apr 7, 2015 at 10:39 PM, Joe Perches <joe@perches.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@numascale.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];
 		}

--