On 2023/08/08 18:43, Alex Bennée wrote:
Richard Henderson <richard.hender...@linaro.org> writes:Use this as extra protection for the guest mapping over any qemu host mappings. Tested-by: Helge Deller <del...@gmx.de> Reviewed-by: Helge Deller <del...@gmx.de> Reviewed-by: Akihiko Odaki <akihiko.od...@daynix.com> Signed-off-by: Richard Henderson <richard.hender...@linaro.org> --- linux-user/elfload.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/linux-user/elfload.c b/linux-user/elfload.c index 36e4026f05..1b4bb2d5af 100644 --- a/linux-user/elfload.c +++ b/linux-user/elfload.c @@ -3147,8 +3147,11 @@ static void load_elf_image(const char *image_name, int image_fd, /* * Reserve address space for all of this. * - * In the case of ET_EXEC, we supply MAP_FIXED so that we get - * exactly the address range that is required. + * In the case of ET_EXEC, we supply MAP_FIXED_NOREPLACE so that we get + * exactly the address range that is required. Without reserved_va, + * the guest address space is not isolated. We have attempted to avoid + * conflict with the host program itself via probe_guest_base, but using + * MAP_FIXED_NOREPLACE instead of MAP_FIXED provides an extra check. * * Otherwise this is ET_DYN, and we are searching for a location * that can hold the memory space required. If the image is @@ -3160,7 +3163,7 @@ static void load_elf_image(const char *image_name, int image_fd, */ load_addr = target_mmap(loaddr, (size_t)hiaddr - loaddr + 1, PROT_NONE, MAP_PRIVATE | MAP_ANON | MAP_NORESERVE | - (ehdr->e_type == ET_EXEC ? MAP_FIXED : 0), + (ehdr->e_type == ET_EXEC ? MAP_FIXED_NOREPLACE : 0), -1, 0);We should probably also check the result == load_addr for the places where MAP_FIXED_NOREPLACE isn't supported as we have this in osdep.h: #ifndef MAP_FIXED_NOREPLACE #define MAP_FIXED_NOREPLACE 0 #endif See 2667e069e7 (linux-user: don't use MAP_FIXED in pgd_find_hole_fallback)
It assumes target_mmap() emulates MAP_FIXED_NOREPLACE when the host does not support it as commit e69e032d1a ("linux-user: Use MAP_FIXED_NOREPLACE for do_brk()") already does, but defining MAP_FIXED_NOREPLACE zero breaks such emulation. I wrote a fix:
https://patchew.org/QEMU/20230808115242.73025-1-akihiko.od...@daynix.com/
if (load_addr == -1) { goto exit_mmap;
