On Wed, 2021-04-14 at 10:38 +0200, Cornelia Huck wrote: > 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.
Yes, I saw it only with uprobes, and then it leads only to a process crash, not to a kernel crash. Thanks!