Re: [PATCH 4/9] x86/pv: Implement pv_hypercall() in C

["Jan Beulich" <JBeulich@suse.com>]

>>> On 18.07.16 at 11:51, <andrew.cooper3@citrix.com> wrote:
> +long pv_hypercall(struct cpu_user_regs *regs)
> +{
> +    struct vcpu *curr = current;
> +#ifndef NDEBUG
> +    unsigned long old_rip = regs->rip;
> +#endif
> +    long ret;
> +    uint32_t eax = regs->eax;
> +
> +    ASSERT(curr->arch.flags & TF_kernel_mode);

I'm afraid TF_kernel_mode can't be relied on for 32-bit guests, so
this needs to move into the if() below.

> +    if ( (eax >= NR_hypercalls) || !hypercall_table[eax] )
> +         return -ENOSYS;
> +
> +    if ( !is_pv_32bit_vcpu(curr) )
> +    {
> +        unsigned long rdi = regs->rdi;
> +        unsigned long rsi = regs->rsi;
> +        unsigned long rdx = regs->rdx;
> +        unsigned long r10 = regs->r10;
> +        unsigned long r8 = regs->r8;
> +        unsigned long r9 = regs->r9;
> +
> +#ifndef NDEBUG
> +        /* Deliberately corrupt parameter regs not used by this hypercall. */
> +        switch ( hypercall_args_table[eax] )
> +        {
> +        case 0: rdi = 0xdeadbeefdeadf00dUL;
> +        case 1: rsi = 0xdeadbeefdeadf00dUL;
> +        case 2: rdx = 0xdeadbeefdeadf00dUL;
> +        case 3: r10 = 0xdeadbeefdeadf00dUL;
> +        case 4: r8 = 0xdeadbeefdeadf00dUL;
> +        case 5: r9 = 0xdeadbeefdeadf00dUL;

Without comments, aren't these going to become 5 new Coverity
issues?

> +        }
> +#endif
> +        if ( unlikely(tb_init_done) )
> +        {
> +            unsigned long args[6] = { rdi, rsi, rdx, r10, r8, r9 };
> +
> +            __trace_hypercall(TRC_PV_HYPERCALL_V2, eax, args);
> +        }
> +
> +        ret = hypercall_table[eax](rdi, rsi, rdx, r10, r8, r9);
> +
> +#ifndef NDEBUG
> +        if ( regs->rip == old_rip )
> +        {
> +            /* Deliberately corrupt parameter regs used by this hypercall. */
> +            switch ( hypercall_args_table[eax] )
> +            {
> +            case 6: regs->r9  = 0xdeadbeefdeadf00dUL;
> +            case 5: regs->r8  = 0xdeadbeefdeadf00dUL;
> +            case 4: regs->r10 = 0xdeadbeefdeadf00dUL;
> +            case 3: regs->edx = 0xdeadbeefdeadf00dUL;
> +            case 2: regs->esi = 0xdeadbeefdeadf00dUL;
> +            case 1: regs->edi = 0xdeadbeefdeadf00dUL;

For consistency with earlier code, lease use rdx, rsi, and rdi here.

> +#ifndef NDEBUG
> +        if ( regs->rip == old_rip )
> +        {
> +            /* Deliberately corrupt parameter regs used by this hypercall. */
> +            switch ( compat_hypercall_args_table[eax] )
> +            {
> +            case 6: regs->ebp = 0xdeadf00d;
> +            case 5: regs->edi = 0xdeadf00d;
> +            case 4: regs->esi = 0xdeadf00d;
> +            case 3: regs->edx = 0xdeadf00d;
> +            case 2: regs->ecx = 0xdeadf00d;
> +            case 1: regs->ebx = 0xdeadf00d;

Please use 32-bit stores here.

> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -25,70 +25,10 @@ UNLIKELY_START(ne, msi_check)
>          LOAD_C_CLOBBERED compat=1 ax=0
>  UNLIKELY_END(msi_check)
>  
> -        movl  UREGS_rax(%rsp),%eax
>          GET_CURRENT(bx)
>  
> -        cmpl  $NR_hypercalls,%eax
> -        jae   compat_bad_hypercall
> -#ifndef NDEBUG
> -        /* Deliberately corrupt parameter regs not used by this hypercall. */
> -        pushq UREGS_rbx(%rsp); pushq %rcx; pushq %rdx; pushq %rsi; pushq %rdi
> -        pushq UREGS_rbp+5*8(%rsp)
> -        leaq  compat_hypercall_args_table(%rip),%r10
> -        movl  $6,%ecx
> -        subb  (%r10,%rax,1),%cl
> -        movq  %rsp,%rdi
> -        movl  $0xDEADBEEF,%eax
> -        rep   stosq
> -        popq  %r8 ; popq  %r9 ; xchgl %r8d,%r9d /* Args 5&6: zero extend */
> -        popq  %rdx; popq  %rcx; xchgl %edx,%ecx /* Args 3&4: zero extend */
> -        popq  %rdi; popq  %rsi; xchgl %edi,%esi /* Args 1&2: zero extend */
> -        movl  UREGS_rax(%rsp),%eax
> -        pushq %rax
> -        pushq UREGS_rip+8(%rsp)
> -#define SHADOW_BYTES 16 /* Shadow EIP + shadow hypercall # */
> -#else
> -        /* Relocate argument registers and zero-extend to 64 bits. */
> -        xchgl %ecx,%esi              /* Arg 2, Arg 4 */
> -        movl  %edx,%edx              /* Arg 3        */
> -        movl  %edi,%r8d              /* Arg 5        */
> -        movl  %ebp,%r9d              /* Arg 6        */
> -        movl  UREGS_rbx(%rsp),%edi   /* Arg 1        */
> -#define SHADOW_BYTES 0  /* No on-stack shadow state */
> -#endif
> -        cmpb  $0,tb_init_done(%rip)
> -UNLIKELY_START(ne, compat_trace)
> -        call  __trace_hypercall_entry
> -        /* Restore the registers that __trace_hypercall_entry clobbered. */
> -        movl  UREGS_rax+SHADOW_BYTES(%rsp),%eax   /* Hypercall #  */
> -        movl  UREGS_rbx+SHADOW_BYTES(%rsp),%edi   /* Arg 1        */
> -        movl  UREGS_rcx+SHADOW_BYTES(%rsp),%esi   /* Arg 2        */
> -        movl  UREGS_rdx+SHADOW_BYTES(%rsp),%edx   /* Arg 3        */
> -        movl  UREGS_rsi+SHADOW_BYTES(%rsp),%ecx   /* Arg 4        */
> -        movl  UREGS_rdi+SHADOW_BYTES(%rsp),%r8d   /* Arg 5        */
> -        movl  UREGS_rbp+SHADOW_BYTES(%rsp),%r9d   /* Arg 6        */
> -#undef SHADOW_BYTES
> -UNLIKELY_END(compat_trace)
> -        leaq  compat_hypercall_table(%rip),%r10
> -        PERFC_INCR(hypercalls, %rax, %rbx)
> -        callq *(%r10,%rax,8)
> -#ifndef NDEBUG
> -        /* Deliberately corrupt parameter regs used by this hypercall. */
> -        popq  %r10         # Shadow RIP
> -        cmpq  %r10,UREGS_rip+8(%rsp)
> -        popq  %rcx         # Shadow hypercall index
> -        jne   compat_skip_clobber /* If RIP has changed then don't clobber. */
> -        leaq  compat_hypercall_args_table(%rip),%r10
> -        movb  (%r10,%rcx,1),%cl
> -        movl  $0xDEADBEEF,%r10d
> -        testb %cl,%cl; jz compat_skip_clobber; movl %r10d,UREGS_rbx(%rsp)
> -        cmpb  $2, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rcx(%rsp)
> -        cmpb  $3, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rdx(%rsp)
> -        cmpb  $4, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rsi(%rsp)
> -        cmpb  $5, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rdi(%rsp)
> -        cmpb  $6, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rbp(%rsp)
> -compat_skip_clobber:
> -#endif
> +        mov   %rsp, %rdi
> +        call  pv_hypercall
>          movl  %eax,UREGS_rax(%rsp)       # save the return value

To follow the HVM model, this should also move into C.

Jan

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