Re: dtracing unlink

[RVP <rvp%SDF.ORG@localhost>]

On Tue, 31 Oct 2023, bch wrote:

> This should be better:
>
> Index: cddl/osnet/dev/dtrace/amd64/dtrace_asm.S
> ==================================================================
> --- cddl/osnet/dev/dtrace/amd64/dtrace_asm.S
> +++ cddl/osnet/dev/dtrace/amd64/dtrace_asm.S
> @@ -215,12 +215,14 @@
>        pushq   %rbp
>        movq    %rsp, %rbp
>
>        xchgq   %rdi, %rsi              /* make %rsi source, %rdi dest */
>        movq    %rdx, %rcx              /* load count */
> +       callq smap_disable
>        repz                            /* repeat for count ... */
>        smovb                           /*   move from %ds:rsi to %ed:rdi */
> +       callq smap_enable
>        leave
>        ret
>        END(dtrace_copy)
>
> /*
> @@ -230,10 +232,11 @@
> */
>        ENTRY(dtrace_copystr)
>        pushq   %rbp
>        movq    %rsp, %rbp
>
> +       callq smap_disable
> 0:
>        movb    (%rdi), %al             /* load from source */
>        movb    %al, (%rsi)             /* store to destination */
>        addq    $1, %rdi                /* increment source pointer */
>        addq    $1, %rsi                /* increment destination pointer */
> @@ -246,10 +249,11 @@
>        jnz     2f
> 1:
>        cmpq    $0, %rdx
>        jne     0b
> 2:
> +       callq smap_enable
>        leave
>        ret
>
>        END(dtrace_copystr)
>
> @@ -256,50 +260,60 @@
> /*
> uintptr_t
> dtrace_fulword(void *addr)
> */
>        ENTRY(dtrace_fulword)
> +       callq smap_disable
>        movq    (%rdi), %rax
> +       callq smap_enable
>        ret
>        END(dtrace_fulword)
>
> /*
> uint8_t
> dtrace_fuword8_nocheck(void *addr)
> */
>        ENTRY(dtrace_fuword8_nocheck)
> +       callq smap_disable
>        xorq    %rax, %rax
>        movb    (%rdi), %al
> +       callq smap_enable
>        ret
>        END(dtrace_fuword8_nocheck)
>
> /*
> uint16_t
> dtrace_fuword16_nocheck(void *addr)
> */
>        ENTRY(dtrace_fuword16_nocheck)
> +       callq smap_disable
>        xorq    %rax, %rax
>        movw    (%rdi), %ax
> +       callq smap_enable
>        ret
>        END(dtrace_fuword16_nocheck)
>
> /*
> uint32_t
> dtrace_fuword32_nocheck(void *addr)
> */
>        ENTRY(dtrace_fuword32_nocheck)
> +       callq smap_disable
>        xorq    %rax, %rax
>        movl    (%rdi), %eax
> +       callq smap_enable
>        ret
>        END(dtrace_fuword32_nocheck)
>
> /*
> uint64_t
> dtrace_fuword64_nocheck(void *addr)
> */
>        ENTRY(dtrace_fuword64_nocheck)
> +       callq smap_disable
>        movq    (%rdi), %rax
> +       callq smap_enable
>        ret
>        END(dtrace_fuword64_nocheck)
>
> /*
> void

I think we can just use SMAP_DISABLE/SMAP_ENABLE like in the standard
copyinstr() in sys/arch/amd64/amd64/copy.S. The kernel will hotpatch
the correct instructions after checking CPU features very early.

See:

sys/arch/x86/x86/patch.c

-RVP

PS. bch: you should skip the HTML in your emails: none of your messages
have ended up on the mailing-list :)