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From: Andrew Donnellan <ajd@linux.ibm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Cc: "linux-hardening@vger.kernel.org"
	<linux-hardening@vger.kernel.org>,
	"cmr@bluescreens.de" <cmr@bluescreens.de>,
	"ruscur@russell.cc" <ruscur@russell.cc>
Subject: Re: [RFC PATCH 1/6] powerpc/64s: Fix assembly to support larger values of THREAD_SIZE
Date: Wed, 26 Apr 2023 17:03:28 +1000	[thread overview]
Message-ID: <3963fc4a8a27c1cd03b1ba3d0b23f6adc843214d.camel@linux.ibm.com> (raw)
In-Reply-To: <204dee71-e3c3-e974-e8b4-ee6015cc7e3b@csgroup.eu>

On Fri, 2022-11-04 at 17:51 +0000, Christophe Leroy wrote:
> 
> 
> Le 04/11/2022 à 18:27, Andrew Donnellan a écrit :
> > When CONFIG_VMAP_STACK is enabled, we set THREAD_SIZE to be at
> > least the
> > size of a page.
> > 
> > There's a few bits of assembly in the book3s64 code that use
> > THREAD_SIZE in
> > immediate mode instructions, which can only take an operand of up
> > to 16
> > bits signed, which isn't quite large enough.
> > 
> > Fix these spots to use a scratch register or use two immediate mode
> > instructions instead, so we can later enable VMAP_STACK.
> > 
> > Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
> > ---
> >   arch/powerpc/include/asm/asm-compat.h   | 2 ++
> >   arch/powerpc/kernel/entry_64.S          | 4 +++-
> >   arch/powerpc/kernel/irq.c               | 8 ++++++--
> >   arch/powerpc/kernel/misc_64.S           | 4 +++-
> >   arch/powerpc/kvm/book3s_hv_rmhandlers.S | 3 ++-
> >   5 files changed, 16 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/asm-compat.h
> > b/arch/powerpc/include/asm/asm-compat.h
> > index 2bc53c646ccd..30dd7813bf3b 100644
> > --- a/arch/powerpc/include/asm/asm-compat.h
> > +++ b/arch/powerpc/include/asm/asm-compat.h
> > @@ -11,6 +11,7 @@
> >   #define PPC_LL                stringify_in_c(ld)
> >   #define PPC_STL               stringify_in_c(std)
> >   #define PPC_STLU      stringify_in_c(stdu)
> > +#define PPC_STLUX      stringify_in_c(stdux)
> >   #define PPC_LCMPI     stringify_in_c(cmpdi)
> >   #define PPC_LCMPLI    stringify_in_c(cmpldi)
> >   #define PPC_LCMP      stringify_in_c(cmpd)
> > @@ -45,6 +46,7 @@
> >   #define PPC_LL                stringify_in_c(lwz)
> >   #define PPC_STL               stringify_in_c(stw)
> >   #define PPC_STLU      stringify_in_c(stwu)
> > +#define PPC_STLUX      stringify_in_c(stwux)
> >   #define PPC_LCMPI     stringify_in_c(cmpwi)
> >   #define PPC_LCMPLI    stringify_in_c(cmplwi)
> >   #define PPC_LCMP      stringify_in_c(cmpw)
> > diff --git a/arch/powerpc/kernel/entry_64.S
> > b/arch/powerpc/kernel/entry_64.S
> > index 3e2e37e6ecab..af25db6e0205 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -238,7 +238,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
> >         /* Note: this uses SWITCH_FRAME_SIZE rather than
> > INT_FRAME_SIZE
> >            because we don't need to leave the 288-byte ABI gap at
> > the
> >            top of the kernel stack. */
> > -       addi    r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE
> > +       li      r9,0
> > +       ori     r9,r9,THREAD_SIZE-SWITCH_FRAME_SIZE
> > +       add     r7,r7,r9
> 
> So you assume THREAD_SIZE is never more than 64k ? Is that a valid 
> assumption ?

It looks like PPC_PAGE_SHIFT can be up to 18, which would make
THREAD_SIZE 256K, but that's only if you have 256K pages, which is a
44x specific feature. Otherwise AFAICT you can't get THREAD_SHIFT
larger than 16 and therefore THREAD_SIZE <= 64K.


> 
> What about the below instead:
> 
>         addis   r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE@ha
>         addi    r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE@l

That looks better anyway, thanks.

> 
> >   
> >         /*
> >          * PMU interrupts in radix may come in here. They will use
> > r1, not
> > diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> > index 9ede61a5a469..098cf6adceec 100644
> > --- a/arch/powerpc/kernel/irq.c
> > +++ b/arch/powerpc/kernel/irq.c
> > @@ -204,7 +204,9 @@ static __always_inline void
> > call_do_softirq(const void *sp)
> >   {
> >         /* Temporarily switch r1 to sp, call __do_softirq() then
> > restore r1. */
> >         asm volatile (
> > -                PPC_STLU "     %%r1, %[offset](%[sp])  ;"
> > +               "li             %%r0, 0                 ;"
> > +               "ori            %%r0, %%r0, %[offset]   ;"
> 
> Same, you assume offset to be max 64k, is that correct ?
> 
> What about
>                 lis             r0, offset@h
>                 ori             r0, r0, offset@l
> 
> > +                PPC_STLUX "    %%r1, %[sp], %%r0       ;"
> >                 "mr             %%r1, %[sp]             ;"
> >                 "bl             %[callee]               ;"
> >                  PPC_LL "       %%r1, 0(%%r1)           ;"
> > @@ -256,7 +258,9 @@ static __always_inline void call_do_irq(struct
> > pt_regs *regs, void *sp)
> >   
> >         /* Temporarily switch r1 to sp, call __do_irq() then
> > restore r1. */
> >         asm volatile (
> > -                PPC_STLU "     %%r1, %[offset](%[sp])  ;"
> > +               "li             %%r0, 0                 ;"
> > +               "ori            %%r0, %%r0, %[offset]   ;"
> > +                PPC_STLUX "    %%r1, %[sp], %%r0       ;"
> 
> Same
> 
> >                 "mr             %%r4, %%r1              ;"
> >                 "mr             %%r1, %[sp]             ;"
> >                 "bl             %[callee]               ;"
> > diff --git a/arch/powerpc/kernel/misc_64.S
> > b/arch/powerpc/kernel/misc_64.S
> > index 36184cada00b..ff71b98500a3 100644
> > --- a/arch/powerpc/kernel/misc_64.S
> > +++ b/arch/powerpc/kernel/misc_64.S
> > @@ -384,7 +384,9 @@ _GLOBAL(kexec_sequence)
> >         std     r0,16(r1)
> >   
> >         /* switch stacks to newstack -- &kexec_stack.stack */
> > -       stdu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
> > +       li      r0,0
> > +       ori     r0,r0,THREAD_SIZE-STACK_FRAME_OVERHEAD
> > +       stdux   r1,r3,r0
> 
> Same
> 
> >         mr      r1,r3
> >   
> >         li      r0,0
> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > index 37f50861dd98..d05e3d324f4d 100644
> > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > @@ -2686,7 +2686,8 @@ kvmppc_bad_host_intr:
> >         mr      r9, r1
> >         std     r1, PACAR1(r13)
> >         ld      r1, PACAEMERGSP(r13)
> > -       subi    r1, r1, THREAD_SIZE/2 + INT_FRAME_SIZE
> > +       subi    r1, r1, THREAD_SIZE/2
> > +       subi    r1, r1, INT_FRAME_SIZE
> 
> Same, what about
> 
>         subis   r1, r1, THREAD_SIZE/2 + INT_FRAME_SIZE@ha
>         subi    r1, r1, THREAD_SIZE/2 + INT_FRAME_SIZE@l
> 
> >         std     r9, 0(r1)
> >         std     r0, GPR0(r1)
> >         std     r9, GPR1(r1)

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited

  reply	other threads:[~2023-04-26  7:05 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-04 17:27 [RFC PATCH 0/6] VMAP_STACK support for book3s64 Andrew Donnellan
2022-11-04 17:27 ` [RFC PATCH 1/6] powerpc/64s: Fix assembly to support larger values of THREAD_SIZE Andrew Donnellan
2022-11-04 17:51   ` Christophe Leroy
2023-04-26  7:03     ` Andrew Donnellan [this message]
2022-11-04 17:27 ` [RFC PATCH 2/6] powerpc/64s: Helpers to switch between linear and vmapped stack pointers Andrew Donnellan
2022-11-05  8:00   ` Christophe Leroy
2022-11-05 19:28     ` Christophe Leroy
2022-11-07 12:38     ` Nicholas Piggin
2022-11-04 17:27 ` [RFC PATCH 3/6] powerpc/powernv: Keep MSR in register across OPAL entry/return path Andrew Donnellan
2022-11-04 18:00   ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 4/6] powerpc/powernv: Convert pointers to physical addresses in OPAL call args Andrew Donnellan
2022-11-07  0:00   ` Russell Currey
2022-11-08 16:21   ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 5/6] powerpc/powernv/idle: Convert stack pointer to physical address Andrew Donnellan
2022-11-08 16:17   ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 6/6] powerpc/64s: Enable CONFIG_VMAP_STACK Andrew Donnellan
2022-11-05 17:07   ` Christophe Leroy

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