From: Bin Meng <bmeng.cn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: [PATCH] libfdt: Fix the undefined behavior in fdt_num_mem_rsv()
Date: Tue, 30 Mar 2021 17:56:45 +0800 [thread overview]
Message-ID: <20210330095645.515056-1-bmeng.cn@gmail.com> (raw)
With LLVM 10.0.0+, the following codes in fdt_num_mem_rsv() does not
work any more for an fdt that is at address 0:
for (i = 0; (re = fdt_mem_rsv(fdt, i)) != NULL; i++) {
if (fdt64_ld_(&re->size) == 0)
return i;
}
Due to LLVM's optimization engine utilizing a UB in C, the following
code pattern:
if ((pointer + offset) != NULL)
is transformed into:
if (pointer != NULL)
because if pointer is NULL and offset is non-zero, the result of
(pointer + offset) is UB. So LLVM is free to exploit such UB to
perform some optimization.
In this case, fdt_mem_rsv() gets inlined and returns (pointer + offset).
And LLVM in turns emits codes to check fdt against NULL, which won't
work for fdt at address 0.
Signed-off-by: Bin Meng <bmeng.cn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
libfdt/fdt_ro.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index 17584da..4db4013 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -157,18 +157,26 @@ int fdt_generate_phandle(const void *fdt, uint32_t *phandle)
return 0;
}
-static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
+static bool fdt_is_mem_rsv(const void *fdt, int n)
{
unsigned int offset = n * sizeof(struct fdt_reserve_entry);
unsigned int absoffset = fdt_off_mem_rsvmap(fdt) + offset;
if (!can_assume(VALID_INPUT)) {
if (absoffset < fdt_off_mem_rsvmap(fdt))
- return NULL;
+ return false;
if (absoffset > fdt_totalsize(fdt) -
sizeof(struct fdt_reserve_entry))
- return NULL;
+ return false;
}
+
+ return true;
+}
+
+static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
+{
+ if (!fdt_is_mem_rsv(fdt, n))
+ return NULL;
return fdt_mem_rsv_(fdt, n);
}
@@ -191,7 +199,8 @@ int fdt_num_mem_rsv(const void *fdt)
int i;
const struct fdt_reserve_entry *re;
- for (i = 0; (re = fdt_mem_rsv(fdt, i)) != NULL; i++) {
+ for (i = 0; fdt_is_mem_rsv(fdt, i); i++) {
+ re = fdt_mem_rsv_(fdt, i);
if (fdt64_ld_(&re->size) == 0)
return i;
}
--
2.25.1
next reply other threads:[~2021-03-30 9:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-30 9:56 Bin Meng [this message]
[not found] ` <20210330095645.515056-1-bmeng.cn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2021-04-01 3:25 ` [PATCH] libfdt: Fix the undefined behavior in fdt_num_mem_rsv() David Gibson
[not found] ` <YGU9FH3WccMBrfl1-l+x2Y8Cxqc4e6aEkudXLsA@public.gmane.org>
2021-04-02 4:52 ` Bin Meng
[not found] ` <CAEUhbmVsszFcUC8tEYmJ4djPvyDmXspDg-gb9rYZpm8zWwxc1g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2021-04-08 2:54 ` David Gibson
[not found] ` <YG5wZa/ti6klXEZQ-l+x2Y8Cxqc4e6aEkudXLsA@public.gmane.org>
2021-04-08 3:21 ` Bin Meng
[not found] ` <CAEUhbmWeTpRHPdqMtcNWdF-ORJ0OXcMi1YJeN+KUpbkqGKvFGg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2021-04-20 1:30 ` David Gibson
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