Re: [PATCH] mini-os: correct memory access rights for pvh mode

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Juergen Gross, le sam. 15 août 2020 13:15:57 +0200, a ecrit:
> When running as a PVH guest the memory access rights are not set
> correctly: _PAGE_USER should not be set and CR0.WP should be set.
> Especially CR0.WP is important in order to let the allocate on
> demand feature work, as it requires a page fault when writing to a
> read-only page.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

> ---
>  arch/x86/x86_hvm.S    |  2 +-
>  include/x86/arch_mm.h | 18 ++++++++++++------
>  include/x86/os.h      |  1 +
>  3 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/x86_hvm.S b/arch/x86/x86_hvm.S
> index 6e8ad98..42a5f02 100644
> --- a/arch/x86/x86_hvm.S
> +++ b/arch/x86/x86_hvm.S
> @@ -20,7 +20,7 @@ _start:
>  #endif /* __x86_64__ */
>  
>          mov %cr0, %eax
> -        or $X86_CR0_PG, %eax
> +        or $(X86_CR0_PG | X86_CR0_WP), %eax
>          mov %eax, %cr0
>  
>          lgdt gdt_ptr
> diff --git a/include/x86/arch_mm.h b/include/x86/arch_mm.h
> index cbbeb21..ffbec5a 100644
> --- a/include/x86/arch_mm.h
> +++ b/include/x86/arch_mm.h
> @@ -171,17 +171,23 @@ typedef unsigned long pgentry_t;
>  #define _PAGE_PSE      CONST(0x080)
>  #define _PAGE_GLOBAL   CONST(0x100)
>  
> +#ifdef CONFIG_PARAVIRT
> +#define PAGE_USER _PAGE_USER
> +#else
> +#define PAGE_USER CONST(0)
> +#endif
> +
>  #if defined(__i386__)
>  #define L1_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED)
>  #define L1_PROT_RO (_PAGE_PRESENT|_PAGE_ACCESSED)
> -#define L2_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY |_PAGE_USER)
> +#define L2_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY |PAGE_USER)
>  #define L3_PROT (_PAGE_PRESENT)
>  #elif defined(__x86_64__)
> -#define L1_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_USER)
> -#define L1_PROT_RO (_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_USER)
> -#define L2_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER)
> -#define L3_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER)
> -#define L4_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER)
> +#define L1_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|PAGE_USER)
> +#define L1_PROT_RO (_PAGE_PRESENT|_PAGE_ACCESSED|PAGE_USER)
> +#define L2_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|PAGE_USER)
> +#define L3_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|PAGE_USER)
> +#define L4_PROT (_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|PAGE_USER)
>  #endif /* __i386__ || __x86_64__ */
>  
>  /* flags for ioremap */
> diff --git a/include/x86/os.h b/include/x86/os.h
> index a73b63e..46a824d 100644
> --- a/include/x86/os.h
> +++ b/include/x86/os.h
> @@ -27,6 +27,7 @@
>  #define MSR_EFER          0xc0000080
>  #define _EFER_LME         8             /* Long mode enable */
>  
> +#define X86_CR0_WP        0x00010000    /* Write protect */
>  #define X86_CR0_PG        0x80000000    /* Paging */
>  #define X86_CR4_PAE       0x00000020    /* enable physical address extensions */
>  #define X86_CR4_OSFXSR    0x00000200    /* enable fast FPU save and restore */
> -- 
> 2.26.2
> 

-- 
Samuel
<y> la vraie vie, c'est quand le prompt passe de $ à #