linux-kernel - Re: [PATCH v3 3/6] EDAC/fsl_ddr: Fix bad bit shift operations

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Message-ID: <20241022094429.GFZxdz_QNHHr_DCPp3@fat_crate.local>
Date: Tue, 22 Oct 2024 11:44:29 +0200
From: Borislav Petkov <bp@...en8.de>
To: Frank Li <Frank.Li@....com>
Cc: York Sun <york.sun@....com>, Tony Luck <tony.luck@...el.com>,
	James Morse <james.morse@....com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, linux-edac@...r.kernel.org,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
	devicetree@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	Priyanka Singh <priyanka.singh@....com>,
	Sherry Sun <sherry.sun@....com>, Li Yang <leoyang.li@....com>
Subject: Re: [PATCH v3 3/6] EDAC/fsl_ddr: Fix bad bit shift operations

On Wed, Oct 16, 2024 at 04:31:11PM -0400, Frank Li wrote:
> From: Priyanka Singh <priyanka.singh@....com>
> 
> Fix undefined behavior caused by left-shifting a negative value in the
> expression:
> 
>     cap_high ^ (1 << (bad_data_bit - 32))
> 
> The variable 'bad_data_bit' ranges from 0 to 63. When 'bad_data_bit' is
> less than 32, 'bad_data_bit - 32' becomes negative, and left-shifting by a
> negative value in C is undefined behavior.
> 
> Fix this by combining 'cap_high' and 'cap_low' into a 64-bit variable.
> 
> Fixes: ea2eb9a8b620 ("EDAC, fsl-ddr: Separate FSL DDR driver from MPC85xx")
> Signed-off-by: Priyanka Singh <priyanka.singh@....com>
> Reviewed-by: Sherry Sun <sherry.sun@....com>

You can't keep Reviewed-by tags when you change a patch considerably: Documentation/process/submitting-patches.rst

> Signed-off-by: Li Yang <leoyang.li@....com>

What does that SOB tag mean?

> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>  drivers/edac/fsl_ddr_edac.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/edac/fsl_ddr_edac.c b/drivers/edac/fsl_ddr_edac.c
> index 7a9fb1202f1a0..846a4ba25342a 100644
> --- a/drivers/edac/fsl_ddr_edac.c
> +++ b/drivers/edac/fsl_ddr_edac.c
> @@ -328,6 +328,9 @@ static void fsl_mc_check(struct mem_ctl_info *mci)
>  	 * TODO: Add support for 32-bit wide buses
>  	 */
>  	if ((err_detect & DDR_EDE_SBE) && (bus_width == 64)) {
> +		u64 cap = (u64)cap_high << 32 | (u64)cap_low;
> +		u32 s = syndrome;
> +
>  		sbe_ecc_decode(cap_high, cap_low, syndrome,
>  				&bad_data_bit, &bad_ecc_bit);
>  
> @@ -338,11 +341,15 @@ static void fsl_mc_check(struct mem_ctl_info *mci)
>  			fsl_mc_printk(mci, KERN_ERR,
>  				"Faulty ECC bit: %d\n", bad_ecc_bit);
>  
> +		if (bad_data_bit >= 0)

>= 0 implies != -1, right?

IOW?

diff --git a/drivers/edac/fsl_ddr_edac.c b/drivers/edac/fsl_ddr_edac.c
index 846a4ba25342..fe822cb9b562 100644
--- a/drivers/edac/fsl_ddr_edac.c
+++ b/drivers/edac/fsl_ddr_edac.c
@@ -328,24 +328,21 @@ static void fsl_mc_check(struct mem_ctl_info *mci)
 	 * TODO: Add support for 32-bit wide buses
 	 */
 	if ((err_detect & DDR_EDE_SBE) && (bus_width == 64)) {
-		u64 cap = (u64)cap_high << 32 | (u64)cap_low;
+		u64 cap = (u64)cap_high << 32 | cap_low;
 		u32 s = syndrome;
 
 		sbe_ecc_decode(cap_high, cap_low, syndrome,
 				&bad_data_bit, &bad_ecc_bit);
 
-		if (bad_data_bit != -1)
-			fsl_mc_printk(mci, KERN_ERR,
-				"Faulty Data bit: %d\n", bad_data_bit);
-		if (bad_ecc_bit != -1)
-			fsl_mc_printk(mci, KERN_ERR,
-				"Faulty ECC bit: %d\n", bad_ecc_bit);
-
-		if (bad_data_bit >= 0)
+		if (bad_data_bit >= 0) {
+			fsl_mc_printk(mci, KERN_ERR, "Faulty Data bit: %d\n", bad_data_bit);
 			cap ^= 1ULL << bad_data_bit;
+		}
 
-		if (bad_ecc_bit >= 0)
+		if (bad_ecc_bit >= 0) {
+			fsl_mc_printk(mci, KERN_ERR, "Faulty ECC bit: %d\n", bad_ecc_bit);
 			s ^= 1 << bad_ecc_bit;
+		}
 
 		fsl_mc_printk(mci, KERN_ERR,
 			"Expected Data / ECC:\t%#8.8x_%08x / %#2.2x\n",

-- 
Regards/Gruss,
    Boris.

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