| Message ID | 1476786468-2173-3-git-send-email-james.morse@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Oct 18, 2016 at 11:27:47AM +0100, James Morse wrote: > Commit 338d4f49d6f7 ("arm64: kernel: Add support for Privileged Access > Never") enabled PAN by enabling the 'SPAN' feature-bit in SCTLR_EL1. > This means the PSTATE.PAN bit won't be set until the next return to the > kernel from userspace. On a preemptible kernel we may schedule work that > accesses userspace on a CPU before it has done this. > > Now that cpufeature enable() calls are scheduled via stop_machine(), we > can set PSTATE.PAN from the cpu_enable_pan() call. > > Add WARN_ON_ONCE(in_interrupt()) to check the PSTATE value we updated > is not immediately discarded. > > Reported-by: Tony Thompson <anthony.thompson@arm.com> > Reported-by: Vladimir Murzin <vladimir.murzin@arm.com> > Signed-off-by: James Morse <james.morse@arm.com> > > --- > This patch depends on 'arm64: cpufeature: Schedule enable() calls instead > of calling them via IPI', which doesn't apply to linux-stable versions > before v4.8. > > arch/arm64/mm/fault.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 3e9ff9b0c78d..f942ab6cc206 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -29,7 +29,9 @@ > #include <linux/sched.h> > #include <linux/highmem.h> > #include <linux/perf_event.h> > +#include <linux/preempt.h> > > +#include <asm/bug.h> > #include <asm/cpufeature.h> > #include <asm/exception.h> > #include <asm/debug-monitors.h> > @@ -672,7 +674,14 @@ NOKPROBE_SYMBOL(do_debug_exception); > #ifdef CONFIG_ARM64_PAN > int cpu_enable_pan(void *__unused) > { > + /* > + * We modify PSTATE. This won't work from irq context as the PSTATE > + * is discared once we return from the exception. > + */ I fixed the typo in the comment and queued these as fixes. Please take care of stable once these are in mainline. Will
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 3e9ff9b0c78d..f942ab6cc206 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -29,7 +29,9 @@ #include <linux/sched.h> #include <linux/highmem.h> #include <linux/perf_event.h> +#include <linux/preempt.h> +#include <asm/bug.h> #include <asm/cpufeature.h> #include <asm/exception.h> #include <asm/debug-monitors.h> @@ -672,7 +674,14 @@ NOKPROBE_SYMBOL(do_debug_exception); #ifdef CONFIG_ARM64_PAN int cpu_enable_pan(void *__unused) { + /* + * We modify PSTATE. This won't work from irq context as the PSTATE + * is discared once we return from the exception. + */ + WARN_ON_ONCE(in_interrupt()); + config_sctlr_el1(SCTLR_EL1_SPAN, 0); + asm(SET_PSTATE_PAN(1)); return 0; } #endif /* CONFIG_ARM64_PAN */
Commit 338d4f49d6f7 ("arm64: kernel: Add support for Privileged Access Never") enabled PAN by enabling the 'SPAN' feature-bit in SCTLR_EL1. This means the PSTATE.PAN bit won't be set until the next return to the kernel from userspace. On a preemptible kernel we may schedule work that accesses userspace on a CPU before it has done this. Now that cpufeature enable() calls are scheduled via stop_machine(), we can set PSTATE.PAN from the cpu_enable_pan() call. Add WARN_ON_ONCE(in_interrupt()) to check the PSTATE value we updated is not immediately discarded. Reported-by: Tony Thompson <anthony.thompson@arm.com> Reported-by: Vladimir Murzin <vladimir.murzin@arm.com> Signed-off-by: James Morse <james.morse@arm.com> --- This patch depends on 'arm64: cpufeature: Schedule enable() calls instead of calling them via IPI', which doesn't apply to linux-stable versions before v4.8. arch/arm64/mm/fault.c | 9 +++++++++ 1 file changed, 9 insertions(+)