Re: [PATCH v5 0/4] linux-user: Fix siginfo_t contents when jumping to non-readable pages

[Vivian Wang]

On 8/17/22 23:05, Ilya Leoshkevich wrote:

> Hi,
>
> I noticed that when we get a SEGV due to jumping to non-readable
> memory, sometimes si_addr and program counter in siginfo_t are slightly
> off. I tracked this down to the assumption that translators stop before
> the end of a page, while in reality they may stop right after it.
>

Hi,

Could this be related to issue 1155 [1]? On RISC-V, I'm getting incorrect [m|s]tval/[m|s]epc combinations for page faults in system emulation and incorrect si_addr and program counter on SIGSEGV in user emulation. Since it seems to only affect instructions that cross page boundaries, and RISC-V also has variable length instructions, it seems that I've run into the same problem as what is fixed here.

Could this fix be extended be extended to targets/riscv?

dram

[1]: https://gitlab.com/qemu-project/qemu/-/issues/1155
> Patch 1 fixes an invalidation issue, which may prevent SEGV from
> happening altogether.
> Patches 2-3 fix the main issue on x86_64 and s390x. Many other
> architectures have fixed-size instructions and are not affected.
> Patch 4 adds tests.
>
> Note: this series depends on [1].
>
> Best regards,
> Ilya
>
> v1: https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg00822.html
> v1 -> v2: Fix individual translators instead of translator_loop
>           (Peter).
>
> v2: https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg01079.html
> v2 -> v3: Peek at the next instruction on s390x (Richard).
>           Undo more on i386 (Richard).
>           Check PAGE_EXEC, not PAGE_READ (Peter, Richard).
>
> v3: https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg01306.html
> v3 -> v4: Improve the commit message in patch 1 to better reflect what
>           exactly is being fixed there.
>           Factor out the is_same_page() patch (Richard).
>           Do not touch the common code in the i386 fix (Richard).
>
> v4: https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg01747.html
> v4 -> v5: Drop patch 2.
>           Use a different fix for the invalidation issue based on
>           discussion with Richard [2].
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg02472.html
> [2] https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg02556.html
>
> Ilya Leoshkevich (4):
>   linux-user: Clear tb_jmp_cache on mprotect()
>   target/s390x: Make translator stop before the end of a page
>   target/i386: Make translator stop before the end of a page
>   tests/tcg: Test siginfo_t contents when jumping to non-readable pages
>
>  linux-user/mmap.c                |  14 +++
>  target/i386/tcg/translate.c      |  25 +++++-
>  target/s390x/tcg/translate.c     |  15 +++-
>  tests/tcg/multiarch/noexec.h     | 114 ++++++++++++++++++++++++
>  tests/tcg/s390x/Makefile.target  |   1 +
>  tests/tcg/s390x/noexec.c         | 145 +++++++++++++++++++++++++++++++
>  tests/tcg/x86_64/Makefile.target |   3 +-
>  tests/tcg/x86_64/noexec.c        | 116 +++++++++++++++++++++++++
>  8 files changed, 427 insertions(+), 6 deletions(-)
>  create mode 100644 tests/tcg/multiarch/noexec.h
>  create mode 100644 tests/tcg/s390x/noexec.c
>  create mode 100644 tests/tcg/x86_64/noexec.c
>
>