Re: [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.08.2019 15:42, Andrew Cooper wrote:
> gdt_boot_descr and gdt_48 disagree on how long trampoline_gdt is.
>
> Introduce an end label and have the linker calculate the size, rather than
> hard coding it.
>
> Also, just as with c/s af292b41e9, there is no point forcing the CPU to set
> Access bits.  Fix all remaining GDTs in Xen.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> The trampoline GDT access bits were actually noticed when trying to clean up
> our boot time pagetables and map the trampoline read-only.
> ---
>   xen/arch/x86/boot/head.S          |  2 +-
>   xen/arch/x86/boot/trampoline.S    | 15 ++++++++-------
>   xen/arch/x86/x86_64/kexec_reloc.S |  4 ++--
>   3 files changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
> index 26b680521d..9fdb9b3954 100644
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -129,7 +129,7 @@ multiboot2_header:
>   
>           .word   0
>   gdt_boot_descr:
> -        .word   7*8-1
> +        .word   .Ltramopline_gdt_end - trampoline_gdt - 1
>   gdt_boot_base:
>           .long   sym_offs(trampoline_gdt)
>           .long   0 /* Needed for 64-bit lgdt */
> diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
> index 7c6a2328d2..1761fc1213 100644
> --- a/xen/arch/x86/boot/trampoline.S
> +++ b/xen/arch/x86/boot/trampoline.S
> @@ -63,22 +63,23 @@ trampoline_gdt:
>           /* 0x0000: unused */
>           .quad   0x0000000000000000
>           /* 0x0008: ring 0 code, 32-bit mode */
> -        .quad   0x00cf9a000000ffff
> +        .quad   0x00cf9b000000ffff
>           /* 0x0010: ring 0 code, 64-bit mode */
> -        .quad   0x00af9a000000ffff
> +        .quad   0x00af9b000000ffff
>           /* 0x0018: ring 0 data */
> -        .quad   0x00cf92000000ffff
> +        .quad   0x00cf93000000ffff
>           /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
>           .long   0x0000ffff
> -        .long   0x00009a00
> +        .long   0x00009b00
>           /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
>           .long   0x0000ffff
> -        .long   0x00009200
> +        .long   0x00009300
>           /*
>            * 0x0030: ring 0 Xen data, 16 MiB size, base
>            * address is computed at runtime.
>            */
> -        .quad   0x00c0920000000fff
> +        .quad   0x00c0930000000fff
> +.Ltramopline_gdt_end:
With the typo here fixed

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

But may I talk you into ...

> --- a/xen/arch/x86/x86_64/kexec_reloc.S
> +++ b/xen/arch/x86/x86_64/kexec_reloc.S
> @@ -182,8 +182,8 @@ compat_mode_gdt_desc:
>           .align 8
>   compat_mode_gdt:
>           .quad 0x0000000000000000     /* null                              */
> -        .quad 0x00cf92000000ffff     /* 0x0008 ring 0 data                */
> -        .quad 0x00cf9a000000ffff     /* 0x0010 ring 0 code, compatibility */
> +        .quad 0x00cf93000000ffff     /* 0x0008 ring 0 data                */
> +        .quad 0x00cf9b000000ffff     /* 0x0010 ring 0 code, compatibility */
... introducing a similar "end" label here and using it at
compat_mode_gdt_desc (the R-b above stands with that change)?

Jan

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