Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 9 Sep 2015 15:01:32 -0700 | Subject | Re: [PATCH v4 RESEND] x86/asm/entry/32, selftests: Add 'test_syscall_vdso' test |
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On Mon, Sep 7, 2015 at 8:56 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote: > This new test checks that all x86 registers are preserved across > 32-bit syscalls. It tests syscalls through VDSO (if available) > and through INT 0x80, normally and under ptrace. > > If kernel is a 64-bit one, high registers (r8..r15) are poisoned > before the syscall is called and are checked afterwards. > > They must be either preserved, or cleared to zero (but r11 is special); > r12..15 must be preserved for INT 0x80. > > EFLAGS is checked for changes too, but change there is not > considered to be a bug (paravirt kernels do not preserve > arithmetic flags). > > Run-tested on 64-bit kernel: > > $ ./test_syscall_vdso_32 > [RUN] Executing 6-argument 32-bit syscall via VDSO > [OK] Arguments are preserved across syscall > [NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn > [OK] R8..R15 did not leak kernel data > [RUN] Executing 6-argument 32-bit syscall via INT 80 > [OK] Arguments are preserved across syscall > [OK] R8..R15 did not leak kernel data > [RUN] Running tests under ptrace > [RUN] Executing 6-argument 32-bit syscall via VDSO > [OK] Arguments are preserved across syscall > [OK] R8..R15 did not leak kernel data > [RUN] Executing 6-argument 32-bit syscall via INT 80 > [OK] Arguments are preserved across syscall > [OK] R8..R15 did not leak kernel data > > On 32-bit paravirt kernel: > > $ ./test_syscall_vdso_32 > [NOTE] Not a 64-bit kernel, won't test R8..R15 leaks > [RUN] Executing 6-argument 32-bit syscall via VDSO > [WARN] Flags before=0000000000200ed7 id 0 00 o d i s z 0 a 0 p 1 c > [WARN] Flags after=0000000000200246 id 0 00 i z 0 0 p 1 > [WARN] Flags change=0000000000000c91 0 00 o d s 0 a 0 0 c > [OK] Arguments are preserved across syscall > [RUN] Executing 6-argument 32-bit syscall via INT 80 > [OK] Arguments are preserved across syscall > [RUN] Running tests under ptrace > [RUN] Executing 6-argument 32-bit syscall via VDSO > [OK] Arguments are preserved across syscall > [RUN] Executing 6-argument 32-bit syscall via INT 80 > [OK] Arguments are preserved across syscall > > Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> > CC: Linus Torvalds <torvalds@linux-foundation.org> > CC: Steven Rostedt <rostedt@goodmis.org> > CC: Ingo Molnar <mingo@kernel.org> > CC: Borislav Petkov <bp@alien8.de> > CC: "H. Peter Anvin" <hpa@zytor.com> > CC: Andy Lutomirski <luto@amacapital.net> > CC: Oleg Nesterov <oleg@redhat.com> > CC: Frederic Weisbecker <fweisbec@gmail.com> > CC: Alexei Starovoitov <ast@plumgrid.com> > CC: Will Drewry <wad@chromium.org> > CC: Kees Cook <keescook@chromium.org> > CC: x86@kernel.org > CC: linux-kernel@vger.kernel.org
Acked-by: Andy Lutomirski <luto@kernel.org>
with minor caveats below, none of which are show-stoppers...
> + /* INT80 syscall entrypoint can be used by > + * 64-bit programs too, unlike SYSCALL/SYSENTER. > + * Therefore it must preserve R12+ > + * (they are callee-saved registers in 64-bit C ABI). > + * > + * This was probably historically not intended, > + * but R8..11 are clobbered (cleared to 0). > + * IOW: they are the only registers which aren't > + * preserved across INT80 syscall. > + */ > + if (*r64 == 0 && num <= 11) > + continue;
Ugh. I'll change my big entry patchset to preserve these and maybe to preserve all of the 64-bit regs.
> +int main(int argc, char **argv, char **envp) > +{ > + int exitcode = 0; > + int cs; > + > + asm("\n" > + " movl %%cs, %%eax\n" > + : "=a" (cs) > + ); > + kernel_is_64bit = (cs == 0x23); > + if (!kernel_is_64bit) > + printf("[NOTE]\tNot a 64-bit kernel, won't test R8..R15 leaks\n"); > +
Does this work on Xen? IIRC Xen is quite likely to land you in a funny Xen-specific CS.
If you want to be fancier, you could borrow cs_bitness from sigreturn.c.
> + /* This only works for non-static builds: > + * syscall_addr = dlsym(dlopen("linux-gate.so.1", RTLD_NOW), "__kernel_vsyscall"); > + */ > + syscall_addr = get_syscall(envp); > + > + exitcode += run_syscall_twice(); > + ptrace_me(); > + exitcode += run_syscall_twice(); > + > + return exitcode; > +} > +#endif > diff --git a/tools/testing/selftests/x86/thunks_32.S b/tools/testing/selftests/x86/thunks_32.S > new file mode 100644 > index 0000000..77e9159 > --- /dev/null > +++ b/tools/testing/selftests/x86/thunks_32.S
As a followup, we should rename thunks.S to thunks_64.S or just merge both of them into one file.
--Andy
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