* [PATCH 60/82] powerpc: Refactor intentional wrap-around test
[not found] <20240122235208.work.748-kees@kernel.org>
@ 2024-01-23 0:27 ` Kees Cook
2024-02-12 5:38 ` Michael Ellerman
0 siblings, 1 reply; 2+ messages in thread
From: Kees Cook @ 2024-01-23 0:27 UTC (permalink / raw)
To: linux-hardening
Cc: Vasant Hegde, Kees Cook, Mahesh Salgaonkar, Gustavo A. R. Silva,
Aneesh Kumar K.V, dingsenjie, Nicholas Piggin, Justin Stitt,
Naveen N. Rao, linuxppc-dev, linux-kernel, Bill Wendling
In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:
VAR + value < VAR
Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.
Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.
Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Cc: dingsenjie <dingsenjie@yulong.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/powerpc/platforms/powernv/opal-prd.c | 2 +-
arch/powerpc/xmon/xmon.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/platforms/powernv/opal-prd.c b/arch/powerpc/platforms/powernv/opal-prd.c
index b66b06efcef1..eaf95dc82925 100644
--- a/arch/powerpc/platforms/powernv/opal-prd.c
+++ b/arch/powerpc/platforms/powernv/opal-prd.c
@@ -51,7 +51,7 @@ static bool opal_prd_range_is_valid(uint64_t addr, uint64_t size)
struct device_node *parent, *node;
bool found;
- if (addr + size < addr)
+ if (add_would_overflow(addr, size))
return false;
parent = of_find_node_by_path("/reserved-memory");
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index b3b94cd37713..b91fdda49434 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3252,7 +3252,7 @@ memzcan(void)
} else if (!ok && ook)
printf("%.8lx\n", a - mskip);
ook = ok;
- if (a + mskip < a)
+ if (add_would_overflow(a, mskip))
break;
}
if (ook)
--
2.34.1
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