diff options
author | Peter Maydell <peter.maydell@linaro.org> | 2011-04-18 16:34:24 +0100 |
---|---|---|
committer | Riku Voipio <riku.voipio@iki.fi> | 2011-06-21 20:29:01 +0300 |
commit | 00faf08c951fcc351467faac5697307a86edb077 (patch) | |
tree | 3a85f8adb1b674999861b2cee5ff658e2d41d86b | |
parent | f3ed1f5d476bfc18c4b2e27bf2386f54c98561f1 (diff) |
linux-user: Don't use MAP_FIXED in do_brk()
Since mmap() with MAP_FIXED will map over the top of existing mappings,
it's a bad idea to use it to implement brk(), because brk() with a
large size is likely to overwrite important things like qemu itself
or the host libc. So we drop MAP_FIXED and handle "mapped but at
different address" as an error case instead.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
-rw-r--r-- | linux-user/syscall.c | 29 |
1 files changed, 20 insertions, 9 deletions
diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 5cb27c7f9f..b9757306ac 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -735,23 +735,34 @@ abi_long do_brk(abi_ulong new_brk) return target_brk; } - /* We need to allocate more memory after the brk... */ + /* We need to allocate more memory after the brk... Note that + * we don't use MAP_FIXED because that will map over the top of + * any existing mapping (like the one with the host libc or qemu + * itself); instead we treat "mapped but at wrong address" as + * a failure and unmap again. + */ new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page + 1); mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size, PROT_READ|PROT_WRITE, - MAP_ANON|MAP_FIXED|MAP_PRIVATE, 0, 0)); + MAP_ANON|MAP_PRIVATE, 0, 0)); + + if (mapped_addr == brk_page) { + target_brk = new_brk; + return target_brk; + } else if (mapped_addr != -1) { + /* Mapped but at wrong address, meaning there wasn't actually + * enough space for this brk. + */ + target_munmap(mapped_addr, new_alloc_size); + mapped_addr = -1; + } #if defined(TARGET_ALPHA) /* We (partially) emulate OSF/1 on Alpha, which requires we return a proper errno, not an unchanged brk value. */ - if (is_error(mapped_addr)) { - return -TARGET_ENOMEM; - } + return -TARGET_ENOMEM; #endif - - if (!is_error(mapped_addr)) { - target_brk = new_brk; - } + /* For everything else, return the previous break. */ return target_brk; } |