Messages in this thread | | | Subject | Re: [PATCH v13 15/16] selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write | From | Shuah Khan <> | Date | Fri, 29 May 2020 08:40:42 -0600 |
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On 5/28/20 2:14 PM, Sasha Levin wrote: > From: "Chang S. Bae" <chang.seok.bae@intel.com> > > The test validates that the selector is not changed when a ptracer writes > the ptracee's GS base. > > Originally-by: Andy Lutomirski <luto@kernel.org> > Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> > Reviewed-by: Tony Luck <tony.luck@intel.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Dave Hansen <dave.hansen@intel.com> > Cc: Tony Luck <tony.luck@intel.com> > Cc: Andi Kleen <ak@linux.intel.com> > Signed-off-by: Sasha Levin <sashal@kernel.org> > --- > tools/testing/selftests/x86/fsgsbase.c | 21 +++++++++++++++------ > 1 file changed, 15 insertions(+), 6 deletions(-) > > diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c > index 15a329da59fa..950a48b2e366 100644 > --- a/tools/testing/selftests/x86/fsgsbase.c > +++ b/tools/testing/selftests/x86/fsgsbase.c > @@ -465,7 +465,7 @@ static void test_ptrace_write_gsbase(void) > wait(&status); > > if (WSTOPSIG(status) == SIGTRAP) { > - unsigned long gs, base; > + unsigned long gs; > unsigned long gs_offset = USER_REGS_OFFSET(gs); > unsigned long base_offset = USER_REGS_OFFSET(gs_base); > > @@ -481,7 +481,6 @@ static void test_ptrace_write_gsbase(void) > err(1, "PTRACE_POKEUSER"); > > gs = ptrace(PTRACE_PEEKUSER, child, gs_offset, NULL); > - base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL); > > /* > * In a non-FSGSBASE system, the nonzero selector will load > @@ -489,11 +488,21 @@ static void test_ptrace_write_gsbase(void) > * selector value is changed or not by the GSBASE write in > * a ptracer. > */ > - if (gs == 0 && base == 0xFF) { > - printf("[OK]\tGS was reset as expected\n"); > - } else { > + if (gs != *shared_scratch) { > nerrs++; > - printf("[FAIL]\tGS=0x%lx, GSBASE=0x%lx (should be 0, 0xFF)\n", gs, base); > + printf("[FAIL]\tGS changed to %lx\n", gs); > + > + /* > + * On older kernels, poking a nonzero value into the > + * base would zero the selector. On newer kernels, > + * this behavior has changed -- poking the base > + * changes only the base and, if FSGSBASE is not > + * available, this may not effect. > + */ > + if (gs == 0) > + printf("\tNote: this is expected behavior on older kernels.\n");
Let's add what is "this" for context in this message.
> + } else { > + printf("[OK]\tGS remained 0x%hx\n", *shared_scratch); > } > } > >
thanks, -- Shuah
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