The previous change, 2d385be6152, assumed !PAGE_VALID meant that the page would be unmapped by the elf image. However, since we reserved the entire image space via mmap, PAGE_VALID will always be set. Instead, assume PROT_NONE for the same condition.
Furthermore, assume bss is only ever present for writable segments, and that there is no page overlap between PT_LOAD segments. Instead of an assert, return false to indicate failure. Cc: qemu-sta...@nongnu.org Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1854 Fixes: 2d385be6152 ("linux-user: Do not adjust zero_bss for host page size") Signed-off-by: Richard Henderson <richard.hender...@linaro.org> --- linux-user/elfload.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) diff --git a/linux-user/elfload.c b/linux-user/elfload.c index a5b28fa3e7..7bc7bcec19 100644 --- a/linux-user/elfload.c +++ b/linux-user/elfload.c @@ -2308,21 +2308,40 @@ static bool zero_bss(abi_ulong start_bss, abi_ulong end_bss, int prot) { abi_ulong align_bss; + /* We only expect writable bss; the code segment shouldn't need this. */ + if (!(prot & PROT_WRITE)) { + return false; + } + align_bss = TARGET_PAGE_ALIGN(start_bss); end_bss = TARGET_PAGE_ALIGN(end_bss); if (start_bss < align_bss) { int flags = page_get_flags(start_bss); - if (!(flags & PAGE_VALID)) { - /* Map the start of the bss. */ + if (!(flags & PAGE_BITS)) { + /* + * The whole address space of the executable was reserved + * at the start, therefore all pages will be VALID. + * But assuming there are no PROT_NONE PT_LOAD segments, + * a PROT_NONE page means no data all bss, and we can + * simply extend the new anon mapping back to the start + * of the page of bss. + */ align_bss -= TARGET_PAGE_SIZE; - } else if (flags & PAGE_WRITE) { - /* The page is already mapped writable. */ - memset(g2h_untagged(start_bss), 0, align_bss - start_bss); } else { - /* Read-only zeros? */ - g_assert_not_reached(); + /* + * The start of the bss shares a page with something. + * The only thing that we expect is the data section, + * which would already be marked writable. + * Overlapping the RX code segment seems malformed. + */ + if (!(flags & PAGE_WRITE)) { + return false; + } + + /* The page is already mapped and writable. */ + memset(g2h_untagged(start_bss), 0, align_bss - start_bss); } } -- 2.34.1
