Re: [PATCH v7 07/11] arm64: unify native/compat instruction skipping

Kees Cook
2020-02-26T21:41:22Z

On Wed, Feb 26, 2020 at 03:57:10PM +0000, Mark Brown wrote:
> From: Dave Martin <Dave.Martin@arm.com>
>
> Skipping of an instruction on AArch32 works a bit differently from
> AArch64, mainly due to the different CPSR/PSTATE semantics.
>
> Currently arm64_skip_faulting_instruction() is only suitable for
> AArch64, and arm64_compat_skip_faulting_instruction() handles the IT
> state machine but is local to traps.c.
>
> Since manual instruction skipping implies a trap, it's a relatively
> slow path.
>
> So, make arm64_skip_faulting_instruction() handle both compat and
> native, and get rid of the arm64_compat_skip_faulting_instruction()
> special case.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/kernel/traps.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index b8c714dda851..bc9f4292bfc3 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -272,6 +272,8 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
> }
> }
>
> +static void advance_itstate(struct pt_regs *regs);
> +
> void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> {
> regs->pc += size;
> @@ -282,6 +284,9 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> */
> if (user_mode(regs))
> user_fastforward_single_step(current);
> +
> + if (regs->pstate & PSR_MODE32_BIT)
> + advance_itstate(regs);
> }
>
> static LIST_HEAD(undef_hook);
> @@ -644,19 +649,12 @@ static void advance_itstate(struct pt_regs *regs)
> compat_set_it_state(regs, it);
> }
>
> -static void arm64_compat_skip_faulting_instruction(struct pt_regs *regs,
> - unsigned int sz)
> -{
> - advance_itstate(regs);
> - arm64_skip_faulting_instruction(regs, sz);
> -}
> -
> static void compat_cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
> {
> int reg = (esr & ESR_ELx_CP15_32_ISS_RT_MASK) >> ESR_ELx_CP15_32_ISS_RT_SHIFT;
>
> pt_regs_write_reg(regs, reg, arch_timer_get_rate());
> - arm64_compat_skip_faulting_instruction(regs, 4);
> + arm64_skip_faulting_instruction(regs, 4);
> }
>
> static const struct sys64_hook cp15_32_hooks[] = {
> @@ -676,7 +674,7 @@ static void compat_cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
>
> pt_regs_write_reg(regs, rt, lower_32_bits(val));
> pt_regs_write_reg(regs, rt2, upper_32_bits(val));
> - arm64_compat_skip_faulting_instruction(regs, 4);
> + arm64_skip_faulting_instruction(regs, 4);
> }
>
> static const struct sys64_hook cp15_64_hooks[] = {
> @@ -697,7 +695,7 @@ void do_cp15instr(unsigned int esr, struct pt_regs *regs)
> * There is no T16 variant of a CP access, so we
> * always advance PC by 4 bytes.
> */
> - arm64_compat_skip_faulting_instruction(regs, 4);
> + arm64_skip_faulting_instruction(regs, 4);
> return;
> }
>
> --
> 2.20.1
>

--
Kees Cook