[PATCH 10/12] sata: sx4: fix pdc20621_get_from_dimm() on 64-bit

Arnd Bergmann
2024-03-26T14:53:54Z

From: Arnd Bergmann <arnd@arndb.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@arndb.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