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runtime: handle sysReserve returning a pointer below the arena

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In mheap.sysAlloc, if an allocation at arena_used would exceed
arena_end (but wouldn't yet push us past arena_start+_MaxArean32), it
trie to extend the arena reservation by another 256 MB. It extends the
arena by calling sysReserve, which, on 32-bit, calls mmap without
MAP_FIXED, which means the address is just a hint and the kernel can
put the mapping wherever it wants. In particular, mmap may choose an
address below arena_start (the kernel also chose arena_start, so there
could be lots of space below it). Currently, we don't detect this case
and, if it happens, mheap.sysAlloc will corrupt arena_end and
arena_used then return the low pointer to mheap.grow, which will crash
when it attempts to index in to h_spans with an underflowed index.

Fix this by checking not only that that p+p_size isn't too high, but
that p isn't too low.

Fixes #13143.

Change-Id: I8d0f42bd1484460282a83c6f1a6f8f0df7fb2048
Reviewed-on: https://go-review.googlesource.com/16927
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Austin Clements 2015-11-15 23:13:16 -05:00
parent 97dc591534
commit 0de59c27eb
1 changed files with 1 additions and 1 deletions
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2
src/runtime/malloc.go
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@ -404,7 +404,7 @@ func (h *mheap) sysAlloc(n uintptr) unsafe.Pointer {
if p == h.arena_end {
h.arena_end = new_end
h.arena_reserved = reserved
} else if p+p_size <= h.arena_start+_MaxArena32 {
} else if h.arena_start <= p && p+p_size <= h.arena_start+_MaxArena32 {
// Keep everything page-aligned.
// Our pages are bigger than hardware pages.
h.arena_end = p + p_size