The following commit has been merged into the x86/fsgsbase branch of tip: Commit-ID: 291fd83569e10f3d305cd8adb62f6ec00f759dc6 Gitweb: https://git.kernel.org/tip/291fd83569e10f3d305cd8adb62f6ec00f759dc6 Author: Chang S. Bae <chang.seok....@intel.com> AuthorDate: Thu, 28 May 2020 16:14:01 -04:00 Committer: Thomas Gleixner <t...@linutronix.de> CommitterDate: Thu, 18 Jun 2020 15:47:06 +02:00
selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write The test validates that the selector is not changed when a ptracer writes the ptracee's GS base. Originally-by: Andy Lutomirski <l...@kernel.org> Signed-off-by: Chang S. Bae <chang.seok....@intel.com> Signed-off-by: Sasha Levin <sas...@kernel.org> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Reviewed-by: Tony Luck <tony.l...@intel.com> Link: https://lkml.kernel.org/r/20200528201402.1708239-16-sas...@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 15a329d..950a48b 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"); + } else { + printf("[OK]\tGS remained 0x%hx\n", *shared_scratch); } }
