linux-kernel - [PATCH v3] EDAC/i10nm: Fix an inappropriate shift exponent

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Message-Id: <20230704095939.119620-1-koba.ko@canonical.com>
Date:   Tue,  4 Jul 2023 17:59:39 +0800
From:   Koba Ko <koba.ko@...onical.com>
To:     Borislav Petkov <bp@...en8.de>, Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Richter <rric@...nel.org>, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] EDAC/i10nm: Fix an inappropriate shift exponent

A surprising value was determined after a read failure from a DIMM.

Software analyses pointed a data processing issue out.
`UBSAN: shift-out-of-bounds in drivers/edac/skx_common.c:369:16
 shift exponent -66 is negative`

A special value combination could not be handled so far.

Check if an invalid value was detected by a call of the function “skx_get_dimm_attr”.
* Print a corresponding error message in this case.
* Return zero then directly from the function “skx_get_dimm_info”.

Fixes: 4ec656bdf43a ("EDAC, skx_edac: Add EDAC driver for Skylake")
Signed-off-by: Koba Ko <koba.ko@...onical.com>
---
v3: According to Markus' comments, simplify and polish the summary and add `Fixes:`
v2: make error-print explicitly

 drivers/edac/skx_common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/edac/skx_common.c b/drivers/edac/skx_common.c
index 2a00e0503f0d5..ac61db72d2e6b 100644
--- a/drivers/edac/skx_common.c
+++ b/drivers/edac/skx_common.c
@@ -330,7 +330,7 @@ static int skx_get_dimm_attr(u32 reg, int lobit, int hibit, int add,
 	u32 val = GET_BITFIELD(reg, lobit, hibit);
 
 	if (val < minval || val > maxval) {
-		edac_dbg(2, "bad %s = %d (raw=0x%x)\n", name, val, reg);
+		skx_printk(KERN_ERR, "bad %s = %d (raw=0x%x)\n", name, val, reg);
 		return -EINVAL;
 	}
 	return val + add;
@@ -351,6 +351,8 @@ int skx_get_dimm_info(u32 mtr, u32 mcmtr, u32 amap, struct dimm_info *dimm,
 	ranks = numrank(mtr);
 	rows = numrow(mtr);
 	cols = imc->hbm_mc ? 6 : numcol(mtr);
+	if (ranks == -EINVAL || rows == -EINVAL || cols == -EINVAL)
+		return 0;
 
 	if (imc->hbm_mc) {
 		banks = 32;
-- 
2.25.1