kselftest: arm64: add helper get_current_context

Introduce a new common utility function get_current_context() which can be
used to grab a ucontext without the help of libc, and also to detect if
such ucontext has been successfully used by placing it on the stack as a
fake sigframe.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Cristian Marussi 2019-10-25 18:57:11 +01:00 committed by Catalin Marinas
parent 837387a2cb
commit 34306b05d3
3 changed files with 134 additions and 1 deletions

View File

@ -72,8 +72,12 @@ struct tdescr {
/* optional sa_flags for the installed handler */
int sa_flags;
ucontext_t saved_uc;
/* used by get_current_ctx() */
size_t live_sz;
ucontext_t *live_uc;
volatile sig_atomic_t live_uc_valid;
/* optional test private data */
void *priv;
void *priv;
/* a custom setup: called alternatively to default_setup */
int (*setup)(struct tdescr *td);

View File

@ -11,14 +11,19 @@
#include <linux/auxvec.h>
#include <ucontext.h>
#include <asm/unistd.h>
#include <kselftest.h>
#include "test_signals.h"
#include "test_signals_utils.h"
#include "testcases/testcases.h"
extern struct tdescr *current;
static int sig_copyctx = SIGTRAP;
static char const *const feats_names[FMAX_END] = {
" SSBS ",
};
@ -154,6 +159,20 @@ static bool handle_signal_ok(struct tdescr *td,
return true;
}
static bool handle_signal_copyctx(struct tdescr *td,
siginfo_t *si, void *uc)
{
/* Mangling PC to avoid loops on original BRK instr */
((ucontext_t *)uc)->uc_mcontext.pc += 4;
memcpy(td->live_uc, uc, td->live_sz);
ASSERT_GOOD_CONTEXT(td->live_uc);
td->live_uc_valid = 1;
fprintf(stderr,
"GOOD CONTEXT grabbed from sig_copyctx handler\n");
return true;
}
static void default_handler(int signum, siginfo_t *si, void *uc)
{
if (current->sig_unsupp && signum == current->sig_unsupp &&
@ -165,6 +184,9 @@ static void default_handler(int signum, siginfo_t *si, void *uc)
} else if (current->sig_ok && signum == current->sig_ok &&
handle_signal_ok(current, si, uc)) {
fprintf(stderr, "Handled SIG_OK\n");
} else if (signum == sig_copyctx && current->live_uc &&
handle_signal_copyctx(current, si, uc)) {
fprintf(stderr, "Handled SIG_COPYCTX\n");
} else {
if (signum == SIGALRM && current->timeout) {
fprintf(stderr, "-- Timeout !\n");
@ -219,6 +241,15 @@ static inline int default_trigger(struct tdescr *td)
int test_init(struct tdescr *td)
{
if (td->sig_trig == sig_copyctx) {
fprintf(stdout,
"Signal %d is RESERVED, cannot be used as a trigger. Aborting\n",
sig_copyctx);
return 0;
}
/* just in case */
unblock_signal(sig_copyctx);
td->minsigstksz = getauxval(AT_MINSIGSTKSZ);
if (!td->minsigstksz)
td->minsigstksz = MINSIGSTKSZ;

View File

@ -4,6 +4,10 @@
#ifndef __TEST_SIGNALS_UTILS_H__
#define __TEST_SIGNALS_UTILS_H__
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include "test_signals.h"
int test_init(struct tdescr *td);
@ -17,4 +21,98 @@ static inline bool feats_ok(struct tdescr *td)
return (td->feats_required & td->feats_supported) == td->feats_required;
}
/*
* Obtaining a valid and full-blown ucontext_t from userspace is tricky:
* libc getcontext does() not save all the regs and messes with some of
* them (pstate value in particular is not reliable).
*
* Here we use a service signal to grab the ucontext_t from inside a
* dedicated signal handler, since there, it is populated by Kernel
* itself in setup_sigframe(). The grabbed context is then stored and
* made available in td->live_uc.
*
* As service-signal is used a SIGTRAP induced by a 'brk' instruction,
* because here we have to avoid syscalls to trigger the signal since
* they would cause any SVE sigframe content (if any) to be removed.
*
* Anyway this function really serves a dual purpose:
*
* 1. grab a valid sigcontext into td->live_uc for result analysis: in
* such case it returns 1.
*
* 2. detect if, somehow, a previously grabbed live_uc context has been
* used actively with a sigreturn: in such a case the execution would have
* magically resumed in the middle of this function itself (seen_already==1):
* in such a case return 0, since in fact we have not just simply grabbed
* the context.
*
* This latter case is useful to detect when a fake_sigreturn test-case has
* unexpectedly survived without hitting a SEGV.
*
* Note that the case of runtime dynamically sized sigframes (like in SVE
* context) is still NOT addressed: sigframe size is supposed to be fixed
* at sizeof(ucontext_t).
*/
static __always_inline bool get_current_context(struct tdescr *td,
ucontext_t *dest_uc)
{
static volatile bool seen_already;
assert(td && dest_uc);
/* it's a genuine invocation..reinit */
seen_already = 0;
td->live_uc_valid = 0;
td->live_sz = sizeof(*dest_uc);
memset(dest_uc, 0x00, td->live_sz);
td->live_uc = dest_uc;
/*
* Grab ucontext_t triggering a SIGTRAP.
*
* Note that:
* - live_uc_valid is declared volatile sig_atomic_t in
* struct tdescr since it will be changed inside the
* sig_copyctx handler
* - the additional 'memory' clobber is there to avoid possible
* compiler's assumption on live_uc_valid and the content
* pointed by dest_uc, which are all changed inside the signal
* handler
* - BRK causes a debug exception which is handled by the Kernel
* and finally causes the SIGTRAP signal to be delivered to this
* test thread. Since such delivery happens on the ret_to_user()
* /do_notify_resume() debug exception return-path, we are sure
* that the registered SIGTRAP handler has been run to completion
* before the execution path is restored here: as a consequence
* we can be sure that the volatile sig_atomic_t live_uc_valid
* carries a meaningful result. Being in a single thread context
* we'll also be sure that any access to memory modified by the
* handler (namely ucontext_t) will be visible once returned.
* - note that since we are using a breakpoint instruction here
* to cause a SIGTRAP, the ucontext_t grabbed from the signal
* handler would naturally contain a PC pointing exactly to this
* BRK line, which means that, on return from the signal handler,
* or if we place the ucontext_t on the stack to fake a sigreturn,
* we'll end up in an infinite loop of BRK-SIGTRAP-handler.
* For this reason we take care to artificially move forward the
* PC to the next instruction while inside the signal handler.
*/
asm volatile ("brk #666"
: "+m" (*dest_uc)
:
: "memory");
/*
* If we get here with seen_already==1 it implies the td->live_uc
* context has been used to get back here....this probably means
* a test has failed to cause a SEGV...anyway live_uc does not
* point to a just acquired copy of ucontext_t...so return 0
*/
if (seen_already) {
fprintf(stdout,
"Unexpected successful sigreturn detected: live_uc is stale !\n");
return 0;
}
seen_already = 1;
return td->live_uc_valid;
}
#endif