| Message ID | 20191101221150.116536-14-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4,01/17] arm64: mm: avoid x18 in idmap_kpti_install_ng_mappings | expand |
On 2019-11-01 23:21, Sami Tolvanen wrote: > Don't lose the current task's shadow stack when the CPU is suspended. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > Reviewed-by: Kees Cook <keescook@chromium.org> > --- > arch/arm64/include/asm/suspend.h | 2 +- > arch/arm64/mm/proc.S | 10 ++++++++++ > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/suspend.h > b/arch/arm64/include/asm/suspend.h > index 8939c87c4dce..0cde2f473971 100644 > --- a/arch/arm64/include/asm/suspend.h > +++ b/arch/arm64/include/asm/suspend.h > @@ -2,7 +2,7 @@ > #ifndef __ASM_SUSPEND_H > #define __ASM_SUSPEND_H > > -#define NR_CTX_REGS 12 > +#define NR_CTX_REGS 13 > #define NR_CALLEE_SAVED_REGS 12 > > /* > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > index fdabf40a83c8..5616dc52a033 100644 > --- a/arch/arm64/mm/proc.S > +++ b/arch/arm64/mm/proc.S > @@ -49,6 +49,8 @@ > * cpu_do_suspend - save CPU registers context > * > * x0: virtual address of context pointer > + * > + * This must be kept in sync with struct cpu_suspend_ctx in > <asm/suspend.h>. > */ > ENTRY(cpu_do_suspend) > mrs x2, tpidr_el0 > @@ -73,6 +75,9 @@ alternative_endif > stp x8, x9, [x0, #48] > stp x10, x11, [x0, #64] > stp x12, x13, [x0, #80] > +#ifdef CONFIG_SHADOW_CALL_STACK > + str x18, [x0, #96] > +#endif Do we need the #ifdefery here? We didn't add that to the KVM path, and I'd feel better having a single behaviour, specially when NR_CTX_REGS is unconditionally sized to hold 13 regs. > ret > ENDPROC(cpu_do_suspend) > > @@ -89,6 +94,11 @@ ENTRY(cpu_do_resume) > ldp x9, x10, [x0, #48] > ldp x11, x12, [x0, #64] > ldp x13, x14, [x0, #80] > +#ifdef CONFIG_SHADOW_CALL_STACK > + ldr x18, [x0, #96] > + /* Clear the SCS pointer from the state buffer */ > + str xzr, [x0, #96] > +#endif > msr tpidr_el0, x2 > msr tpidrro_el0, x3 > msr contextidr_el1, x4 Thanks, M.
On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@kernel.org> wrote: > > ENTRY(cpu_do_suspend) > > mrs x2, tpidr_el0 > > @@ -73,6 +75,9 @@ alternative_endif > > stp x8, x9, [x0, #48] > > stp x10, x11, [x0, #64] > > stp x12, x13, [x0, #80] > > +#ifdef CONFIG_SHADOW_CALL_STACK > > + str x18, [x0, #96] > > +#endif > > Do we need the #ifdefery here? We didn't add that to the KVM path, > and I'd feel better having a single behaviour, specially when > NR_CTX_REGS is unconditionally sized to hold 13 regs. I'm fine with dropping the ifdefs here in v5 unless someone objects to this. Sami
On Mon, Nov 4, 2019 at 1:38 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@kernel.org> wrote: > > > ENTRY(cpu_do_suspend) > > > mrs x2, tpidr_el0 > > > @@ -73,6 +75,9 @@ alternative_endif > > > stp x8, x9, [x0, #48] > > > stp x10, x11, [x0, #64] > > > stp x12, x13, [x0, #80] > > > +#ifdef CONFIG_SHADOW_CALL_STACK > > > + str x18, [x0, #96] > > > +#endif > > > > Do we need the #ifdefery here? We didn't add that to the KVM path, > > and I'd feel better having a single behaviour, specially when > > NR_CTX_REGS is unconditionally sized to hold 13 regs. > > I'm fine with dropping the ifdefs here in v5 unless someone objects to this. Oh, yeah I guess it would be good to be consistent. Rather than drop the ifdefs, would you (Marc) be ok with conditionally setting NR_CTX_REGS based on CONFIG_SHADOW_CALL_STACK, and doing so in KVM? (So 3 ifdefs, rather than 0)? Without any conditionals or comments, it's not clear why x18 is being saved and restored (unless git blame survives, or a comment is added in place of the ifdefs in v6).
On Mon, Nov 4, 2019 at 1:59 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Mon, Nov 4, 2019 at 1:38 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@kernel.org> wrote: > > > > ENTRY(cpu_do_suspend) > > > > mrs x2, tpidr_el0 > > > > @@ -73,6 +75,9 @@ alternative_endif > > > > stp x8, x9, [x0, #48] > > > > stp x10, x11, [x0, #64] > > > > stp x12, x13, [x0, #80] > > > > +#ifdef CONFIG_SHADOW_CALL_STACK > > > > + str x18, [x0, #96] > > > > +#endif > > > > > > Do we need the #ifdefery here? We didn't add that to the KVM path, > > > and I'd feel better having a single behaviour, specially when > > > NR_CTX_REGS is unconditionally sized to hold 13 regs. > > > > I'm fine with dropping the ifdefs here in v5 unless someone objects to this. > > Oh, yeah I guess it would be good to be consistent. Rather than drop > the ifdefs, would you (Marc) be ok with conditionally setting > NR_CTX_REGS based on CONFIG_SHADOW_CALL_STACK, and doing so in KVM? > (So 3 ifdefs, rather than 0)? > > Without any conditionals or comments, it's not clear why x18 is being > saved and restored (unless git blame survives, or a comment is added > in place of the ifdefs in v6). True. Clearing the sleep state buffer in cpu_do_resume is also pointless without CONFIG_SHADOW_CALL_STACK, so if the ifdefs are removed, some kind of an explanation is needed there. Sami
On 2019-11-05 01:11, Sami Tolvanen wrote: > On Mon, Nov 4, 2019 at 1:59 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: >> >> On Mon, Nov 4, 2019 at 1:38 PM Sami Tolvanen >> <samitolvanen@google.com> wrote: >> > >> > On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@kernel.org> >> wrote: >> > > > ENTRY(cpu_do_suspend) >> > > > mrs x2, tpidr_el0 >> > > > @@ -73,6 +75,9 @@ alternative_endif >> > > > stp x8, x9, [x0, #48] >> > > > stp x10, x11, [x0, #64] >> > > > stp x12, x13, [x0, #80] >> > > > +#ifdef CONFIG_SHADOW_CALL_STACK >> > > > + str x18, [x0, #96] >> > > > +#endif >> > > >> > > Do we need the #ifdefery here? We didn't add that to the KVM >> path, >> > > and I'd feel better having a single behaviour, specially when >> > > NR_CTX_REGS is unconditionally sized to hold 13 regs. >> > >> > I'm fine with dropping the ifdefs here in v5 unless someone >> objects to this. >> >> Oh, yeah I guess it would be good to be consistent. Rather than >> drop >> the ifdefs, would you (Marc) be ok with conditionally setting >> NR_CTX_REGS based on CONFIG_SHADOW_CALL_STACK, and doing so in KVM? >> (So 3 ifdefs, rather than 0)? >> >> Without any conditionals or comments, it's not clear why x18 is >> being >> saved and restored (unless git blame survives, or a comment is added >> in place of the ifdefs in v6). > > True. Clearing the sleep state buffer in cpu_do_resume is also > pointless without CONFIG_SHADOW_CALL_STACK, so if the ifdefs are > removed, some kind of an explanation is needed there. I can't imagine the overhead being noticeable, and I certainly value minimizing the testing space. Sticking a comment there should be enough for people hacking on this to understand that this isn't entirely dead code. Thanks, M.
diff --git a/arch/arm64/include/asm/suspend.h b/arch/arm64/include/asm/suspend.h index 8939c87c4dce..0cde2f473971 100644 --- a/arch/arm64/include/asm/suspend.h +++ b/arch/arm64/include/asm/suspend.h @@ -2,7 +2,7 @@ #ifndef __ASM_SUSPEND_H #define __ASM_SUSPEND_H -#define NR_CTX_REGS 12 +#define NR_CTX_REGS 13 #define NR_CALLEE_SAVED_REGS 12 /* diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S index fdabf40a83c8..5616dc52a033 100644 --- a/arch/arm64/mm/proc.S +++ b/arch/arm64/mm/proc.S @@ -49,6 +49,8 @@ * cpu_do_suspend - save CPU registers context * * x0: virtual address of context pointer + * + * This must be kept in sync with struct cpu_suspend_ctx in <asm/suspend.h>. */ ENTRY(cpu_do_suspend) mrs x2, tpidr_el0 @@ -73,6 +75,9 @@ alternative_endif stp x8, x9, [x0, #48] stp x10, x11, [x0, #64] stp x12, x13, [x0, #80] +#ifdef CONFIG_SHADOW_CALL_STACK + str x18, [x0, #96] +#endif ret ENDPROC(cpu_do_suspend) @@ -89,6 +94,11 @@ ENTRY(cpu_do_resume) ldp x9, x10, [x0, #48] ldp x11, x12, [x0, #64] ldp x13, x14, [x0, #80] +#ifdef CONFIG_SHADOW_CALL_STACK + ldr x18, [x0, #96] + /* Clear the SCS pointer from the state buffer */ + str xzr, [x0, #96] +#endif msr tpidr_el0, x2 msr tpidrro_el0, x3 msr contextidr_el1, x4