Re: [Xen-devel] [PATCH] arm/vm_event: get/set registers

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/07/2016 21:05, Tamas K Lengyel wrote:
> Add support for getting/setting registers through vm_event on ARM.
> The set of registers can be expanded in the future to include other registers
> as well if necessary but for now it is limited to TTB/CR/R0/R1, PC and CPSR.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

For the x86 and common bits, Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

However,

> +#include <xen/sched.h>
> +#include <asm/vm_event.h>
> +
> +void vm_event_fill_regs(vm_event_request_t *req)
> +{
> +    const struct cpu_user_regs *regs = guest_cpu_user_regs();
> +
> +    req->data.regs.arm.cpsr = regs->cpsr;
> +    req->data.regs.arm.pc = regs->pc;
> +    req->data.regs.arm.ttbcr = READ_SYSREG(TCR_EL1);
> +    req->data.regs.arm.ttbr0 = READ_SYSREG64(TTBR0_EL1);
> +    req->data.regs.arm.ttbr1 = READ_SYSREG64(TTBR1_EL1);
> +}
> +
> +void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp)
> +{
> +    struct cpu_user_regs *regs = guest_cpu_user_regs();
> +
> +    regs->cpsr = rsp->data.regs.arm.cpsr;
> +    regs->pc = rsp->data.regs.arm.pc;
> +    v->arch.ttbcr = rsp->data.regs.arm.ttbcr;
> +    v->arch.ttbr0 = rsp->data.regs.arm.ttbr0;
> +    v->arch.ttbr1 = rsp->data.regs.arm.ttbr1;

Not knowing anything about ARM, but this looks like it is missing some
sanity/plausibility checks (to protect Xen against accidental clobbering
from the vm_event listener), and some WRITE_SYSREG() to reload the new
values (unless this is done unconditionally later, at which point you
should at least leave a comment here saying so).

~Andrew

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