Re: [PATCH 1/2] RISC-V: Align the shadow stack

[Palmer Dabbelt]

On Tue, 29 Nov 2022 18:47:55 PST (-0800), Khem Raj wrote:
> Hi Palmer
>
> On Tue, Nov 29, 2022 at 6:36 PM Palmer Dabbelt <palmer@xxxxxxxxxxxx> wrote:
> > The standard RISC-V ABIs all require 16-byte stack alignment.  We're
> > only calling that one function on the shadow stack so I doubt it'd
> > result in a real issue, but might as well keep this lined up.
>
> Is 16-byte alignment required on rv32 as well ?

For the standard ABIs that's the case, it's so the Q extension can spill 
without aligning the stack.  There's also at least a proposed embedded 
ABI that has just XLEN (32-bit on rv32) alignment, as the bigger stack 
alignment has an impact on some use cases.

> > Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
> > Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> > ---
> >  arch/riscv/kernel/traps.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > index be54ccea8c47..acdfcacd7e57 100644
> > --- a/arch/riscv/kernel/traps.c
> > +++ b/arch/riscv/kernel/traps.c
> > @@ -206,7 +206,7 @@ static DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
> >   * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used
> >   * to get per-cpu overflow stack(get_overflow_stack).
> >   */
> > -long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)];
> > +long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)] __aligned(16);
> >  asmlinkage unsigned long get_overflow_stack(void)
> >  {
> >         return (unsigned long)this_cpu_ptr(overflow_stack) +
> > --
> > 2.38.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv