* [PATCH RFC 2/2] powerpc/signal: Retire signal trampoline on stack
2021-06-25 10:49 [PATCH 1/2] powerpc/signal: Fix handling of SA_RESTORER sigaction flag Christophe Leroy
@ 2021-06-25 10:49 ` Christophe Leroy
2022-02-04 10:22 ` [PATCH 1/2] powerpc/signal: Fix handling of SA_RESTORER sigaction flag Michael Ellerman
1 sibling, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-06-25 10:49 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman
Cc: linux-kernel, linuxppc-dev
The signal trampoline is either:
- As specified by the caller via SA_RESTORER
- In VDSO if VDSO is properly mapped
- Fallback on user stack
However, nowadays user stack is mapped non executable by default
so the fallback will generate an exec fault.
All other architectures having VDSO except x86 and sh don't install
any fallback trampoline on stack.
Simplify the code by doing the same, remove signal trampoline
on stack. If VDSO is not mapped, a NULL like address will be set
and the user app will gently fault.
If a user application explicitly want's to unmap VDSO, it can
still provide an SA_RESTORER.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/kernel/signal_32.c | 26 +++++++++-------------
arch/powerpc/kernel/signal_64.c | 38 ++++----------------------------
arch/powerpc/perf/callchain_32.c | 5 -----
arch/powerpc/perf/callchain_64.c | 2 --
4 files changed, 14 insertions(+), 57 deletions(-)
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index cf3da1386595..366d07cb42da 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -769,16 +769,13 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
}
/* Save user registers on the stack */
- if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
tramp = (unsigned long)ksig->ka.sa.sa_restorer;
- } else if (tsk->mm->context.vdso) {
+ else if (tsk->mm->context.vdso)
tramp = VDSO32_SYMBOL(tsk->mm->context.vdso, sigtramp_rt32);
- } else {
- tramp = (unsigned long)mctx->mc_pad;
- unsafe_put_user(PPC_RAW_LI(_R0, __NR_rt_sigreturn), &mctx->mc_pad[0], failed);
- unsafe_put_user(PPC_RAW_SC(), &mctx->mc_pad[1], failed);
- asm("dcbst %y0; sync; icbi %y0; sync" :: "Z" (mctx->mc_pad[0]));
- }
+ else
+ tramp = 0;
+
unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
user_access_end();
@@ -867,16 +864,13 @@ int handle_signal32(struct ksignal *ksig, sigset_t *oldset,
else
unsafe_save_user_regs(regs, mctx, tm_mctx, 1, failed);
- if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
tramp = (unsigned long)ksig->ka.sa.sa_restorer;
- } else if (tsk->mm->context.vdso) {
+ else if (tsk->mm->context.vdso)
tramp = VDSO32_SYMBOL(tsk->mm->context.vdso, sigtramp32);
- } else {
- tramp = (unsigned long)mctx->mc_pad;
- unsafe_put_user(PPC_RAW_LI(_R0, __NR_sigreturn), &mctx->mc_pad[0], failed);
- unsafe_put_user(PPC_RAW_SC(), &mctx->mc_pad[1], failed);
- asm("dcbst %y0; sync; icbi %y0; sync" :: "Z" (mctx->mc_pad[0]));
- }
+ else
+ tramp = 0;
+
user_access_end();
regs->link = tramp;
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index fb31a334aca6..39522ebd1137 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -610,32 +610,6 @@ static long restore_tm_sigcontexts(struct task_struct *tsk, struct sigcontext __
}
#endif
-/*
- * Setup the trampoline code on the stack
- */
-static long setup_trampoline(unsigned int syscall, unsigned int __user *tramp)
-{
- int i;
- long err = 0;
-
- /* Call the handler and pop the dummy stackframe*/
- err |= __put_user(PPC_RAW_BCTRL(), &tramp[0]);
- err |= __put_user(PPC_RAW_ADDI(_R1, _R1, __SIGNAL_FRAMESIZE), &tramp[1]);
-
- err |= __put_user(PPC_RAW_LI(_R0, syscall), &tramp[2]);
- err |= __put_user(PPC_RAW_SC(), &tramp[3]);
-
- /* Minimal traceback info */
- for (i=TRAMP_TRACEBACK; i < TRAMP_SIZE ;i++)
- err |= __put_user(0, &tramp[i]);
-
- if (!err)
- flush_icache_range((unsigned long) &tramp[0],
- (unsigned long) &tramp[TRAMP_SIZE]);
-
- return err;
-}
-
/*
* Userspace code may pass a ucontext which doesn't include VSX added
* at the end. We need to check for this case.
@@ -910,16 +884,12 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
tsk->thread.fp_state.fpscr = 0;
/* Set up to return from userspace. */
- if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
regs_set_return_ip(regs, (unsigned long)ksig->ka.sa.sa_restorer);
- } else if (tsk->mm->context.vdso) {
+ else if (tsk->mm->context.vdso)
regs_set_return_ip(regs, VDSO64_SYMBOL(tsk->mm->context.vdso, sigtramp_rt64));
- } else {
- err |= setup_trampoline(__NR_rt_sigreturn, &frame->tramp[0]);
- if (err)
- goto badframe;
- regs_set_return_ip(regs, (unsigned long) &frame->tramp[0]);
- }
+ else
+ regs->nip = 0;
/* Allocate a dummy caller frame for the signal handler. */
newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
diff --git a/arch/powerpc/perf/callchain_32.c b/arch/powerpc/perf/callchain_32.c
index b83c47b7947f..8ab4663cef50 100644
--- a/arch/powerpc/perf/callchain_32.c
+++ b/arch/powerpc/perf/callchain_32.c
@@ -57,8 +57,6 @@ struct rt_signal_frame_32 {
static int is_sigreturn_32_address(unsigned int nip, unsigned int fp)
{
- if (nip == fp + offsetof(struct signal_frame_32, mctx.mc_pad))
- return 1;
if (current->mm->context.vdso &&
nip == VDSO32_SYMBOL(current->mm->context.vdso, sigtramp32))
return 1;
@@ -67,9 +65,6 @@ static int is_sigreturn_32_address(unsigned int nip, unsigned int fp)
static int is_rt_sigreturn_32_address(unsigned int nip, unsigned int fp)
{
- if (nip == fp + offsetof(struct rt_signal_frame_32,
- uc.uc_mcontext.mc_pad))
- return 1;
if (current->mm->context.vdso &&
nip == VDSO32_SYMBOL(current->mm->context.vdso, sigtramp_rt32))
return 1;
diff --git a/arch/powerpc/perf/callchain_64.c b/arch/powerpc/perf/callchain_64.c
index 8d0df4226328..8c7078ff67c2 100644
--- a/arch/powerpc/perf/callchain_64.c
+++ b/arch/powerpc/perf/callchain_64.c
@@ -66,8 +66,6 @@ struct signal_frame_64 {
static int is_sigreturn_64_address(unsigned long nip, unsigned long fp)
{
- if (nip == fp + offsetof(struct signal_frame_64, tramp))
- return 1;
if (current->mm->context.vdso &&
nip == VDSO64_SYMBOL(current->mm->context.vdso, sigtramp_rt64))
return 1;
--
2.25.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH 1/2] powerpc/signal: Fix handling of SA_RESTORER sigaction flag
2021-06-25 10:49 [PATCH 1/2] powerpc/signal: Fix handling of SA_RESTORER sigaction flag Christophe Leroy
2021-06-25 10:49 ` [PATCH RFC 2/2] powerpc/signal: Retire signal trampoline on stack Christophe Leroy
@ 2022-02-04 10:22 ` Michael Ellerman
2022-02-04 11:00 ` Christophe Leroy
1 sibling, 1 reply; 4+ messages in thread
From: Michael Ellerman @ 2022-02-04 10:22 UTC (permalink / raw)
To: Christophe Leroy
Cc: linux-kernel, linuxppc-dev, Tulio Magno Quites Machado Filho
Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> powerpc advertises support of SA_RESTORER sigaction flag.
>
> Make it the truth.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> arch/powerpc/kernel/signal_32.c | 8 ++++++--
> arch/powerpc/kernel/signal_64.c | 4 +++-
> 2 files changed, 9 insertions(+), 3 deletions(-)
Hi Christophe,
I dug into the history a bit on this.
The 32-bit port originally did not define SA_RESTORER in
include/asm-ppc/signal.h, but it was added in 2.1.79.
https://github.com/mpe/linux-fullhistory/commit/4e7e9c0d54ff5725a73d2210a950f8bc0f225073
That commit added SA_RESTORER to the header, added code to get/set it in
sys_sigaction(), but didn't add any code to use it for signal delivery.
The 64-bit port was merged with SA_RESTORER already defined in
include/asm-ppc64/signal.h:
https://github.com/mpe/linux-fullhistory/commit/c3aa9878533e724f639852c3d951e6a169e04081
Similarly there was code to set/get it in sys_sigaction(), but no code
to use it for signal delivery.
Later the two ports were merged, and the headers were moved and
disintegrated into uapi, so we end up today with SA_RESTORER defined in
arch/powerpc/include/uapi/asm/signal.h, but no code to use it.
So essentially we've had SA_RESTORER defined since ancient kernels, but
never actually supported using it for anything.
One problem with enabling it now is there's no way for userspace to
determine if it's on a fixed kernel or not. That makes it unusable for
userspace, unless it does version checks, or is happy to break on all
old kernels (not likely). We could solve that by defining
SA_RESTORER_FIXED or something, but that's slightly gross.
It's also described in the man page as "Not intended for application
use", ie. it's intended for use by libc. I'm not sure there's any value
in adding support for it to the kernel unless we know there's interest
from glibc/musl in using it.
So my inclination is that we should *not* add support for it, rather we
should leave it unimplemented and remove SA_RESTORER from the header.
There's precedent in riscv for not supporting it at all.
cheers
> diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
> index 0608581967f0..cf3da1386595 100644
> --- a/arch/powerpc/kernel/signal_32.c
> +++ b/arch/powerpc/kernel/signal_32.c
> @@ -769,7 +769,9 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
> }
>
> /* Save user registers on the stack */
> - if (tsk->mm->context.vdso) {
> + if (ksig->ka.sa.sa_flags & SA_RESTORER) {
> + tramp = (unsigned long)ksig->ka.sa.sa_restorer;
> + } else if (tsk->mm->context.vdso) {
> tramp = VDSO32_SYMBOL(tsk->mm->context.vdso, sigtramp_rt32);
> } else {
> tramp = (unsigned long)mctx->mc_pad;
> @@ -865,7 +867,9 @@ int handle_signal32(struct ksignal *ksig, sigset_t *oldset,
> else
> unsafe_save_user_regs(regs, mctx, tm_mctx, 1, failed);
>
> - if (tsk->mm->context.vdso) {
> + if (ksig->ka.sa.sa_flags & SA_RESTORER) {
> + tramp = (unsigned long)ksig->ka.sa.sa_restorer;
> + } else if (tsk->mm->context.vdso) {
> tramp = VDSO32_SYMBOL(tsk->mm->context.vdso, sigtramp32);
> } else {
> tramp = (unsigned long)mctx->mc_pad;
> diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> index 1831bba0582e..fb31a334aca6 100644
> --- a/arch/powerpc/kernel/signal_64.c
> +++ b/arch/powerpc/kernel/signal_64.c
> @@ -910,7 +910,9 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
> tsk->thread.fp_state.fpscr = 0;
>
> /* Set up to return from userspace. */
> - if (tsk->mm->context.vdso) {
> + if (ksig->ka.sa.sa_flags & SA_RESTORER) {
> + regs_set_return_ip(regs, (unsigned long)ksig->ka.sa.sa_restorer);
> + } else if (tsk->mm->context.vdso) {
> regs_set_return_ip(regs, VDSO64_SYMBOL(tsk->mm->context.vdso, sigtramp_rt64));
> } else {
> err |= setup_trampoline(__NR_rt_sigreturn, &frame->tramp[0]);
> --
> 2.25.0
^ permalink raw reply [flat|nested] 4+ messages in thread