From: Ammar Faizi ammarfaizi2@gnuweeb.org
The current selftest asserts (%r11 == %rflags) after the 'syscall' returns to user. Such an assertion doesn't apply to the FRED system because in that system the 'syscall' instruction does not set %r11=%rflags and %rcx=%rip.
Handle the FRED case. Now, test that:
- "syscall" in a FRED system doesn't clobber %rcx and %r11. - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.
The 'raise()' function from libc can't be used to control those registers. Therefore, create a syscall wrapper in inline Assembly to fully control them.
Fixes: 660602140103 ("selftests/x86: Add a selftest for SYSRET to noncanonical addresses") Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com Reported-by: Xin Li xin3.li@intel.com Co-developed-by: H. Peter Anvin (Intel) hpa@zytor.com Signed-off-by: H. Peter Anvin (Intel) hpa@zytor.com Signed-off-by: Ammar Faizi ammarfaizi2@gnuweeb.org --- tools/testing/selftests/x86/sysret_rip.c | 114 +++++++++++++++++++++-- 1 file changed, 107 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c index 84d74be1d90207ab..ef3f492d95f6f2a1 100644 --- a/tools/testing/selftests/x86/sysret_rip.c +++ b/tools/testing/selftests/x86/sysret_rip.c @@ -39,6 +39,104 @@ asm ( extern const char test_page[]; static void const *current_test_page_addr = test_page;
+/* Arbitrary values */ +static const unsigned long r11_sentinel = 0xfeedfacedeadbeef; +static const unsigned long rcx_sentinel = 0x5ca1ab1e0b57ac1e; + +/* An arbitrary *valid* RFLAGS value */ +static const unsigned long rflags_sentinel = 0x200a93; + +enum regs_ok { + REGS_UNDEFINED = -1, /* For consistency checker init, never returned */ + REGS_SAVED = 0, /* Registers properly preserved */ + REGS_SYSRET = 1 /* Registers match syscall/sysret */ +}; + +/* + * @rbx should be set to the syscall return %rip. + */ +static void check_regs_result(unsigned long r11, unsigned long rcx, + unsigned long rbx) +{ + static enum regs_ok regs_ok_state = REGS_UNDEFINED; + enum regs_ok ret; + + /* + * REGS_SAVED = %rcx and %r11 preserved (Intel FRED). + * REGS_SYSRET = %rcx and %r11 set to %rflags and %rip. + */ + if (r11 == r11_sentinel && rcx == rcx_sentinel) { + ret = REGS_SAVED; + } else if (r11 == rflags_sentinel && rcx == rbx) { + ret = REGS_SYSRET; + } else { + printf("[FAIL] check_regs_result\n"); + printf(" r11_sentinel = %#lx; %%r11 = %#lx;\n", r11_sentinel, r11); + printf(" rcx_sentinel = %#lx; %%rcx = %#lx;\n", rcx_sentinel, rcx); + printf(" rflags_sentinel = %#lx\n", rflags_sentinel); + exit(1); + } + + + /* + * Test that we don't get a mix of REGS_SAVED and REGS_SYSRET. + * It needs at least calling check_regs_result() twice to assert. + */ + if (regs_ok_state == REGS_UNDEFINED) { + /* + * First time calling check_regs_result(). + */ + regs_ok_state = ret; + } else { + assert(regs_ok_state == ret); + } +} + +static long do_syscall(long nr_syscall, unsigned long arg1, unsigned long arg2, + unsigned long arg3, unsigned long arg4, + unsigned long arg5, unsigned long arg6) +{ + register unsigned long r11 asm("%r11"); + register unsigned long r10 asm("%r10"); + register unsigned long r8 asm("%r8"); + register unsigned long r9 asm("%r9"); + register void *rsp asm("%rsp"); + unsigned long rcx, rbx; + + r11 = r11_sentinel; + rcx = rcx_sentinel; + r10 = arg4; + r8 = arg5; + r9 = arg6; + + asm volatile ( + "pushq %[rflags_sentinel]\n\t" + "popf\n\t" + "leaq 1f(%%rip), %[rbx]\n\t" + "syscall\n" + "1:" + + : "+a" (nr_syscall), + "+r" (r11), + "+c" (rcx), + [rbx] "=b" (rbx), + "+r" (rsp) /* Clobber the redzone */ + + : [rflags_sentinel] "g" (rflags_sentinel), + "D" (arg1), /* %rdi */ + "S" (arg2), /* %rsi */ + "d" (arg3), /* %rdx */ + "r" (r10), + "r" (r8), + "r" (r9) + + : "memory" + ); + + check_regs_result(r11, rcx, rbx); + return nr_syscall; +} + static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), int flags) { @@ -88,24 +186,26 @@ static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+ check_regs_result(ctx->uc_mcontext.gregs[REG_R11], + ctx->uc_mcontext.gregs[REG_RCX], + ctx->uc_mcontext.gregs[REG_RBX]); + /* 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; - - /* R11 and EFLAGS should already match. */ - assert(ctx->uc_mcontext.gregs[REG_EFL] == - ctx->uc_mcontext.gregs[REG_R11]); - sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND); +}
- return; +static void __raise(int sig) +{ + do_syscall(__NR_kill, getpid(), sig, 0, 0, 0, 0); }
static void test_sigreturn_to(unsigned long ip) { rip = ip; printf("[RUN]\tsigreturn to 0x%lx\n", ip); - raise(SIGUSR1); + __raise(SIGUSR1); }
static jmp_buf jmpbuf;