On Tue, 13 Apr 2021 18:52:57 +0200 Ilya Leoshkevich <i...@linux.ibm.com> wrote:
> Hitting an uretprobe in a s390x TCG guest causes a SIGSEGV. What > happens is: > > * uretprobe maps a userspace page containing an invalid instruction. > * uretprobe replaces the target function's return address with the > address of that page. > * When tb_gen_code() is called on that page, tb->size ends up being 0 > (because the page starts with the invalid instruction), which causes > virt_page2 to point to the previous page. > * The previous page is not mapped, so this causes a spurious > translation exception. > > The bug is that tb->size must never be 0: even if there is an illegal > instruction, the instruction bytes that have been looked at must count > towards tb->size. So adjust s390x's translate_one() to act this way > for both illegal instructions and instructions that are known to > generate exceptions. > > Also add an assertion to tb_gen_code() in order to detect such > situations in future. > > Signed-off-by: Ilya Leoshkevich <i...@linux.ibm.com> > --- > > v1: https://lists.nongnu.org/archive/html/qemu-devel/2021-04/msg02037.html > v1 -> v2: Fix target/s390x instead of trying to tolerate tb->size == 0 > in tb_gen_code(). > > accel/tcg/translate-all.c | 1 + > target/s390x/translate.c | 16 +++++++++++----- > 2 files changed, 12 insertions(+), 5 deletions(-) I assume this bug is not usually hit during normal usage, right? It's probably not release critical, so I'll line it up for 6.1 instead.
