Message ID | 20191018161033.261971-4-samitolvanen@google.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | add support for Clang's Shadow Call Stack | expand |
On Fri, 18 Oct 2019 at 18:10, Sami Tolvanen <samitolvanen@google.com> wrote: > > From: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > In preparation of using x18 as a task struct pointer register when > running in the kernel, stop treating it as caller save in the KVM > guest entry/exit code. Currently, the code assumes there is no need > to preserve it for the host, given that it would have been assumed > clobbered anyway by the function call to __guest_enter(). Instead, > preserve its value and restore it upon return. > > Link: https://patchwork.kernel.org/patch/9836891/ > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> You might want to update the commit log to drop the reference to the task struct pointer. > --- > arch/arm64/kvm/hyp/entry.S | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index e5cc8d66bf53..20bd9a20ea27 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -23,6 +23,7 @@ > .pushsection .hyp.text, "ax" > > .macro save_callee_saved_regs ctxt > + str x18, [\ctxt, #CPU_XREG_OFFSET(18)] > stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] > stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] > stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] > @@ -38,6 +39,7 @@ > ldp x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)] > ldp x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)] > ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)] > + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)] > .endm > > /* > @@ -87,12 +89,9 @@ alternative_else_nop_endif > ldp x14, x15, [x18, #CPU_XREG_OFFSET(14)] > ldp x16, x17, [x18, #CPU_XREG_OFFSET(16)] > > - // Restore guest regs x19-x29, lr > + // Restore guest regs x18-x29, lr > restore_callee_saved_regs x18 > > - // Restore guest reg x18 > - ldr x18, [x18, #CPU_XREG_OFFSET(18)] > - > // Do not touch any register after this! > eret > sb > @@ -114,7 +113,7 @@ ENTRY(__guest_exit) > // Retrieve the guest regs x0-x1 from the stack > ldp x2, x3, [sp], #16 // x0, x1 > > - // Store the guest regs x0-x1 and x4-x18 > + // Store the guest regs x0-x1 and x4-x17 > stp x2, x3, [x1, #CPU_XREG_OFFSET(0)] > stp x4, x5, [x1, #CPU_XREG_OFFSET(4)] > stp x6, x7, [x1, #CPU_XREG_OFFSET(6)] > @@ -123,9 +122,8 @@ ENTRY(__guest_exit) > stp x12, x13, [x1, #CPU_XREG_OFFSET(12)] > stp x14, x15, [x1, #CPU_XREG_OFFSET(14)] > stp x16, x17, [x1, #CPU_XREG_OFFSET(16)] > - str x18, [x1, #CPU_XREG_OFFSET(18)] > > - // Store the guest regs x19-x29, lr > + // Store the guest regs x18-x29, lr > save_callee_saved_regs x1 > > get_host_ctxt x2, x3 > -- > 2.23.0.866.gb869b98d4c-goog >
On Fri, 18 Oct 2019 09:10:18 -0700 Sami Tolvanen <samitolvanen@google.com> wrote: > From: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > In preparation of using x18 as a task struct pointer register when > running in the kernel, stop treating it as caller save in the KVM > guest entry/exit code. Currently, the code assumes there is no need > to preserve it for the host, given that it would have been assumed > clobbered anyway by the function call to __guest_enter(). Instead, > preserve its value and restore it upon return. > > Link: https://patchwork.kernel.org/patch/9836891/ > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > arch/arm64/kvm/hyp/entry.S | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index e5cc8d66bf53..20bd9a20ea27 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -23,6 +23,7 @@ > .pushsection .hyp.text, "ax" > > .macro save_callee_saved_regs ctxt > + str x18, [\ctxt, #CPU_XREG_OFFSET(18)] > stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] > stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] > stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] > @@ -38,6 +39,7 @@ > ldp x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)] > ldp x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)] > ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)] > + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)] There is now an assumption that ctxt is x18 (otherwise why would it be out of order?). Please add a comment to that effect. > .endm > > /* > @@ -87,12 +89,9 @@ alternative_else_nop_endif > ldp x14, x15, [x18, #CPU_XREG_OFFSET(14)] > ldp x16, x17, [x18, #CPU_XREG_OFFSET(16)] > > - // Restore guest regs x19-x29, lr > + // Restore guest regs x18-x29, lr > restore_callee_saved_regs x18 Or you could elect another register such as x29 as the base, and keep the above in a reasonable order. > > - // Restore guest reg x18 > - ldr x18, [x18, #CPU_XREG_OFFSET(18)] > - > // Do not touch any register after this! > eret > sb > @@ -114,7 +113,7 @@ ENTRY(__guest_exit) > // Retrieve the guest regs x0-x1 from the stack > ldp x2, x3, [sp], #16 // x0, x1 > > - // Store the guest regs x0-x1 and x4-x18 > + // Store the guest regs x0-x1 and x4-x17 > stp x2, x3, [x1, #CPU_XREG_OFFSET(0)] > stp x4, x5, [x1, #CPU_XREG_OFFSET(4)] > stp x6, x7, [x1, #CPU_XREG_OFFSET(6)] > @@ -123,9 +122,8 @@ ENTRY(__guest_exit) > stp x12, x13, [x1, #CPU_XREG_OFFSET(12)] > stp x14, x15, [x1, #CPU_XREG_OFFSET(14)] > stp x16, x17, [x1, #CPU_XREG_OFFSET(16)] > - str x18, [x1, #CPU_XREG_OFFSET(18)] > > - // Store the guest regs x19-x29, lr > + // Store the guest regs x18-x29, lr > save_callee_saved_regs x1 > > get_host_ctxt x2, x3 Thanks, M.
On Tue, Oct 22, 2019 at 10:22 AM Marc Zyngier <maz@kernel.org> wrote: > > .macro save_callee_saved_regs ctxt > > + str x18, [\ctxt, #CPU_XREG_OFFSET(18)] > > stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] > > stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] > > stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] > > @@ -38,6 +39,7 @@ > > ldp x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)] > > ldp x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)] > > ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)] > > + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)] > > There is now an assumption that ctxt is x18 (otherwise why would it be > out of order?). Please add a comment to that effect. > > - // Restore guest regs x19-x29, lr > > + // Restore guest regs x18-x29, lr > > restore_callee_saved_regs x18 > > Or you could elect another register such as x29 as the base, and keep > the above in a reasonable order. I'm fine with either option. Ard, any thoughts? Sami
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S index e5cc8d66bf53..20bd9a20ea27 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -23,6 +23,7 @@ .pushsection .hyp.text, "ax" .macro save_callee_saved_regs ctxt + str x18, [\ctxt, #CPU_XREG_OFFSET(18)] stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)] stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)] stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)] @@ -38,6 +39,7 @@ ldp x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)] ldp x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)] ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)] + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)] .endm /* @@ -87,12 +89,9 @@ alternative_else_nop_endif ldp x14, x15, [x18, #CPU_XREG_OFFSET(14)] ldp x16, x17, [x18, #CPU_XREG_OFFSET(16)] - // Restore guest regs x19-x29, lr + // Restore guest regs x18-x29, lr restore_callee_saved_regs x18 - // Restore guest reg x18 - ldr x18, [x18, #CPU_XREG_OFFSET(18)] - // Do not touch any register after this! eret sb @@ -114,7 +113,7 @@ ENTRY(__guest_exit) // Retrieve the guest regs x0-x1 from the stack ldp x2, x3, [sp], #16 // x0, x1 - // Store the guest regs x0-x1 and x4-x18 + // Store the guest regs x0-x1 and x4-x17 stp x2, x3, [x1, #CPU_XREG_OFFSET(0)] stp x4, x5, [x1, #CPU_XREG_OFFSET(4)] stp x6, x7, [x1, #CPU_XREG_OFFSET(6)] @@ -123,9 +122,8 @@ ENTRY(__guest_exit) stp x12, x13, [x1, #CPU_XREG_OFFSET(12)] stp x14, x15, [x1, #CPU_XREG_OFFSET(14)] stp x16, x17, [x1, #CPU_XREG_OFFSET(16)] - str x18, [x1, #CPU_XREG_OFFSET(18)] - // Store the guest regs x19-x29, lr + // Store the guest regs x18-x29, lr save_callee_saved_regs x1 get_host_ctxt x2, x3