selftests/x86/fsgsbase: Test ptracer-induced GSBASE write (1b6858d5) · Commits · 戴 / test

tools/testing/selftests/x86/fsgsbase.c

+70 −0

Original line number	Diff line number	Diff line
		@@ -23,6 +23,9 @@
		#include <pthread.h>
		#include <asm/ldt.h>
		#include <sys/mman.h>
		#include <stddef.h>
		#include <sys/ptrace.h>
		#include <sys/wait.h>

		#ifndef __x86_64__
		# error This test is 64-bit only
		@@ -367,6 +370,71 @@ static void test_unexpected_base(void)
		}
		}

		#define USER_REGS_OFFSET(r) offsetof(struct user_regs_struct, r)

		static void test_ptrace_write_gsbase(void)
		{
		int status;
		pid_t child = fork();

		if (child < 0)
		err(1, "fork");

		if (child == 0) {
		printf("[RUN]\tPTRACE_POKE(), write GSBASE from ptracer\n");

		/*
		* Use the LDT setup and fetch the GSBASE from the LDT
		* by switching to the (nonzero) selector (again)
		*/
		do_unexpected_base();
		asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)0x7));

		if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0)
		err(1, "PTRACE_TRACEME");

		raise(SIGTRAP);
		_exit(0);
		}

		wait(&status);

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

		gs = ptrace(PTRACE_PEEKUSER, child, gs_offset, NULL);

		if (gs != 0x7) {
		nerrs++;
		printf("[FAIL]\tGS is not prepared with nonzero\n");
		goto END;
		}

		if (ptrace(PTRACE_POKEUSER, child, base_offset, 0xFF) != 0)
		err(1, "PTRACE_POKEUSER");

		gs = ptrace(PTRACE_PEEKUSER, child, gs_offset, NULL);

		/*
		* In a non-FSGSBASE system, the nonzero selector will load
		* GSBASE (again). But what is tested here is whether the
		* selector value is changed or not by the GSBASE write in
		* a ptracer.
		*/
		if (gs != 0x7) {
		nerrs++;
		printf("[FAIL]\tGS changed to %lx\n", gs);
		} else {
		printf("[OK]\tGS remained 0x7\n");
		}
		}

		END:
		ptrace(PTRACE_CONT, child, NULL, NULL);
		}

		int main()
		{
		pthread_t thread;
		@@ -423,5 +491,7 @@ int main()
		if (pthread_join(thread, NULL) != 0)
		err(1, "pthread_join");

		test_ptrace_write_gsbase();

		return nerrs == 0 ? 0 : 1;
		}

Admin message