When run on a non-FRED system, test the opportunistic SYSRET fast-path. Make sure the %rcx/%r11 clobbering behavior is consistent. When run on a FRED system, test that %rcx/%r11 are preserved when invoking syscall. This is similar to what test_syscall_rcx_r11_consistent() is doing, but with addition it's done via the SIGUSR2 signal handler. Link: https://lore.kernel.org/lkml/8770815f-0f23-d0c5-e56a-d401827842c9@xxxxxxxxx Suggested-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx> Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx> --- On Wed, 25 Jan 2023 00:39:26 -0800, "H. Peter Anvin" wrote: > > /* Set IP and CX to match so that SYSRET can happen. */ > > ctx->uc_mcontext.gregs[REG_RIP] = rip; > > ctx->uc_mcontext.gregs[REG_RCX] = rip; > > It would be interesting to have the syscall handler try both with and > without this (so it would end up doing both IRET and SYSCALL on legacy.) > Perhaps SIGUSR1 versus SIGUSR2... tools/testing/selftests/x86/sysret_rip.c | 37 ++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c index d45b7f0147cd25ad..a1e5ec6f08bcd523 100644 --- a/tools/testing/selftests/x86/sysret_rip.c +++ b/tools/testing/selftests/x86/sysret_rip.c @@ -275,6 +275,28 @@ static void test_syscall_rcx_r11_consistent(void) do_syscall(__NR_getppid, 0, 0, 0, 0, 0, 0); } +static unsigned long usr2_rcx; +static unsigned long usr2_r11; + +static void sigusr2(int sig, siginfo_t *info, void *ctx_void) +{ + ucontext_t *ctx = (ucontext_t*)ctx_void; + + usr2_r11 = ctx->uc_mcontext.gregs[REG_R11]; + usr2_rcx = ctx->uc_mcontext.gregs[REG_RCX]; + + check_regs_result(ctx->uc_mcontext.gregs[REG_R11], + ctx->uc_mcontext.gregs[REG_RCX], + ctx->uc_mcontext.gregs[REG_RBX]); +} + +static void test_sysret_consistent(void) +{ + printf("[RUN]\ttest_sysret_consistent\n"); + __raise(SIGUSR2); + printf("[OK]\tRCX = %#lx; R11 = %#lx\n", usr2_rcx, usr2_r11); +} + int main() { int i; @@ -292,6 +314,21 @@ int main() for (i = 47; i < 64; i++) test_sigreturn_to(1UL<<i); + /* + * + * When run on a non-FRED system, test the SYSRET path. Make + * sure the %rcx/%r11 clobbering behavior is consistent. + * + * When run on a FRED system, test that %rcx/%r11 are preserved + * when invoking syscall. + * + * This is similar to test_syscall_rcx_r11_consistent(), but via + * a signal handler. + */ + sethandler(SIGUSR2, sigusr2, 0); + for (i = 0; i < 32; i++) + test_sysret_consistent(); + clearhandler(SIGUSR1); sethandler(SIGSEGV, sigsegv_for_fallthrough, 0); -- Ammar Faizi
