linux-kernel - [PATCH 10/12] sata: sx4: fix pdc20621_get_from

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Message-Id: <20240326145348.3318887-1-arnd@kernel.org>
Date: Tue, 26 Mar 2024 15:53:37 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: linux-kbuild@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Damien Le Moal <dlemoal@...nel.org>,
	Niklas Cassel <cassel@...nel.org>
Cc: Nicolas Schier <nicolas@...sle.eu>,
	Nathan Chancellor <nathan@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	John Garry <john.g.garry@...cle.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 10/12] sata: sx4: fix pdc20621_get_from_dimm() on 64-bit

From: Arnd Bergmann <arnd@...db.de>

gcc warns about a memcpy() with overlapping pointers because of an
incorrect size calculation:

In file included from include/linux/string.h:369,
                 from drivers/ata/sata_sx4.c:66:
In function 'memcpy_fromio',
    inlined from 'pdc20621_get_from_dimm.constprop' at drivers/ata/sata_sx4.c:962:2:
include/linux/fortify-string.h:97:33: error: '__builtin_memcpy' accessing 4294934464 bytes at offsets 0 and [16, 16400] overlaps 6442385281 bytes at offset -2147450817 [-Werror=restrict]
   97 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:620:9: note: in expansion of macro '__underlying_memcpy'
  620 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:665:26: note: in expansion of macro '__fortify_memcpy_chk'
  665 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
include/asm-generic/io.h:1184:9: note: in expansion of macro 'memcpy'
 1184 |         memcpy(buffer, __io_virt(addr), size);
      |         ^~~~~~

The problem here is the overflow of an unsigned 32-bit number to a
negative that gets converted into a signed 'long', keeping a large
positive number.

Replace the complex calculation with a more readable min() variant
that avoids the warning.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/ata/sata_sx4.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/ata/sata_sx4.c b/drivers/ata/sata_sx4.c
index b51d7a9d0d90..a482741eb181 100644
--- a/drivers/ata/sata_sx4.c
+++ b/drivers/ata/sata_sx4.c
@@ -957,8 +957,7 @@ static void pdc20621_get_from_dimm(struct ata_host *host, void *psource,
 
 	offset -= (idx * window_size);
 	idx++;
-	dist = ((long) (window_size - (offset + size))) >= 0 ? size :
-		(long) (window_size - offset);
+	dist = min(size, window_size - offset);
 	memcpy_fromio(psource, dimm_mmio + offset / 4, dist);
 
 	psource += dist;
@@ -1005,8 +1004,7 @@ static void pdc20621_put_to_dimm(struct ata_host *host, void *psource,
 	readl(mmio + PDC_DIMM_WINDOW_CTLR);
 	offset -= (idx * window_size);
 	idx++;
-	dist = ((long)(s32)(window_size - (offset + size))) >= 0 ? size :
-		(long) (window_size - offset);
+	dist = min(size, window_size - offset);
 	memcpy_toio(dimm_mmio + offset / 4, psource, dist);
 	writel(0x01, mmio + PDC_GENERAL_CTLR);
 	readl(mmio + PDC_GENERAL_CTLR);
-- 
2.39.2