selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE (5e7ec857) · Commits · 戴 / test

This validates that GS selector and base are independently preserved in ptrace commands. Suggested-by:

tools/testing/selftests/x86/fsgsbase.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -465,7 +465,7 @@ static void test_ptrace_write_gsbase(void)
		wait(&status);

		if (WSTOPSIG(status) == SIGTRAP) {
		unsigned long gs;
		unsigned long gs, base;
		unsigned long gs_offset = USER_REGS_OFFSET(gs);
		unsigned long base_offset = USER_REGS_OFFSET(gs_base);

		@@ -481,6 +481,7 @@ 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
		@@ -501,8 +502,14 @@ static void test_ptrace_write_gsbase(void)
		*/
		if (gs == 0)
		printf("\tNote: this is expected behavior on older kernels.\n");
		} else if (have_fsgsbase && (base != 0xFF)) {
		nerrs++;
		printf("[FAIL]\tGSBASE changed to %lx\n", base);
		} else {
		printf("[OK]\tGS remained 0x%hx\n", *shared_scratch);
		printf("[OK]\tGS remained 0x%hx", *shared_scratch);
		if (have_fsgsbase)
		printf(" and GSBASE changed to 0xFF");
		printf("\n");
		}
		}