Re: [Xen-devel] [PATCH] x86/link: Don't merge .init.text and .init.data

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/01/18 14:58, Konrad Rzeszutek Wilk wrote:
> On Thu, Jan 11, 2018 at 02:17:57PM +0000, Andrew Cooper wrote:
>> c/s 1308f0170c merged .init.text and .init.data, because EFI might properly
>> write-protect r/o sections.
>>
>> However, this change makes xen-syms unusable for disassembly analysis.  In
> s/this makes/that made/

Erm.  I'm not sure how to apply that regex, but I've changed to

"However, that change makes xen-syms unusable for disassembly analysis."

~Andrew

>> particular, searching for indirect branches as part of the SP2/Spectre
>> mitigation series.
>>
>> Revert the relevent bits of 1308f0170c and instead modify the EFI relocation
>> code to disable CR0.WP, which is how we deal with relocations in r/o mappings
>> elsewhere.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> with that change above:
>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> ---
>>  xen/arch/x86/efi/efi-boot.h | 12 ++++++++++++
>>  xen/arch/x86/efi/mkreloc.c  |  5 -----
>>  xen/arch/x86/xen.lds.S      |  7 +++----
>>  3 files changed, 15 insertions(+), 9 deletions(-)
>>
>> diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
>> index d30f688..0b5f218 100644
>> --- a/xen/arch/x86/efi/efi-boot.h
>> +++ b/xen/arch/x86/efi/efi-boot.h
>> @@ -47,8 +47,17 @@ extern const struct pe_base_relocs {
>>  
>>  static void __init efi_arch_relocate_image(unsigned long delta)
>>  {
>> +    unsigned long cr0;
>>      const struct pe_base_relocs *base_relocs;
>>  
>> +    /*
>> +     * Conditionally disable CR0.WP in case there are relocations present in
>> +     * read-only mappings.
>> +     */
>> +    cr0 = read_cr0();
>> +    if ( cr0 & X86_CR0_WP )
>> +        write_cr0(cr0 & ~X86_CR0_WP);
>> +
>>      for ( base_relocs = __base_relocs_start; base_relocs < 
>> __base_relocs_end; )
>>      {
>>          unsigned int i = 0, n;
>> @@ -96,6 +105,9 @@ static void __init efi_arch_relocate_image(unsigned long 
>> delta)
>>          }
>>          base_relocs = (const void *)(base_relocs->entries + i + (i & 1));
>>      }
>> +
>> +    if ( cr0 & X86_CR0_WP )
>> +        write_cr0(cr0);
>>  }
>>  
>>  extern const s32 __trampoline_rel_start[], __trampoline_rel_stop[];
>> diff --git a/xen/arch/x86/efi/mkreloc.c b/xen/arch/x86/efi/mkreloc.c
>> index 1aca796..509fd83 100644
>> --- a/xen/arch/x86/efi/mkreloc.c
>> +++ b/xen/arch/x86/efi/mkreloc.c
>> @@ -267,11 +267,6 @@ static void diff_sections(const unsigned char *ptr1, 
>> const unsigned char *ptr2,
>>              exit(3);
>>          }
>>  
>> -        if ( !(sec->flags & COFF_SECTION_WRITEABLE) )
>> -            fprintf(stderr,
>> -                    "Warning: relocation to r/o section %.8s:%08" 
>> PRIxFAST32 "\n",
>> -                    sec->name, i);
>> -
>>          printf("\t.word (%u << 12) | 0x%03" PRIxFAST32 "\n",
>>                 reloc, sec->rva + i - disp - rva);
>>          reloc_size += 2;
>> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
>> index d5e8821..6a7bbb8 100644
>> --- a/xen/arch/x86/xen.lds.S
>> +++ b/xen/arch/x86/xen.lds.S
>> @@ -159,7 +159,7 @@ SECTIONS
>>    __2M_init_start = .;         /* Start of 2M superpages, mapped RWX (boot 
>> only). */
>>    . = ALIGN(PAGE_SIZE);             /* Init code and data */
>>    __init_begin = .;
>> -  .init : {
>> +  .init.text : {
>>         _sinittext = .;
>>         *(.init.text)
>>         /*
>> @@ -169,9 +169,8 @@ SECTIONS
>>          */
>>         *(.altinstr_replacement)
>>         _einittext = .;
>> -
>> -       . = ALIGN(SMP_CACHE_BYTES);
>> -
>> +  } :text
>> +  .init.data : {
>>         *(.init.rodata)
>>         *(.init.rodata.rel)
>>         *(.init.rodata.str*)
>> -- 
>> 2.1.4
>>
>>
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