[CRIU] [PATCH 3/4] vdso: Rework vdso processing files

[Christopher Covington]

Hi Laurent,

On 09/03/2015 10:26 AM, Laurent Dufour wrote:
> There were multiple copy of the same code spread over the different
> architectures handling the vDSO.
> 
> This patch is merging the duplicated code in arch/*/vdso-pie.c and
> arch/*/include/asm/vdso.h in the common files and let only the architecture
> specific part in the arch/*/* files.

Thanks for doing this! I've finally taken these changes for a spin and found
the following issue.

> diff --git a/arch/aarch64/vdso-pie.c b/arch/aarch64/vdso-pie.c
> index c6558378db1d..0f06c2d191d1 100644
> --- a/arch/aarch64/vdso-pie.c
> +++ b/arch/aarch64/vdso-pie.c
> @@ -1,23 +1,10 @@
> -#include <stdlib.h>
> -#include <stdio.h>
>  #include <unistd.h>
> -#include <string.h>
> -#include <elf.h>
> -#include <fcntl.h>
> -#include <errno.h>
> -
> -#include <sys/types.h>
> -#include <sys/stat.h>
> -#include <sys/mman.h>
>  
>  #include "asm/string.h"
>  #include "asm/types.h"
>  
> -#include "compiler.h"
>  #include "syscall.h"
> -#include "image.h"
> -#include "vdso.h"
> -#include "vma.h"
> +#include "parasite-vdso.h"
>  #include "log.h"
>  #include "bug.h"
>  
> @@ -26,7 +13,7 @@
>  #endif
>  #define LOG_PREFIX "vdso: "
>  
> -int vdso_redirect_calls(void *base_to, void *base_from,
> +int vdso_redirect_calls(unsigned long base_to, unsigned long base_from,
>  			struct vdso_symtable *to,
>  			struct vdso_symtable *from)
>  {
> @@ -37,8 +24,8 @@ int vdso_redirect_calls(void *base_to, void *base_from,
>  			continue;
>  
>  		pr_debug("br: %lx/%lx -> %lx/%lx (index %d)\n",
> -			 (unsigned long)base_from, from->symbols[i].offset,
> -			 (unsigned long)base_to, to->symbols[i].offset, i);
> +			 base_from, from->symbols[i].offset,
> +			 base_to, to->symbols[i].offset, i);
>  
>  		write_intraprocedure_branch(base_to + to->symbols[i].offset,
>  					    base_from + from->symbols[i].offset);
> @@ -46,383 +33,3 @@ int vdso_redirect_calls(void *base_to, void *base_from,
>  
>  	return 0;
>  }
> -
> -
> -/* Check if pointer is out-of-bound */
> -static bool __ptr_oob(void *ptr, void *start, size_t size)
> -{
> -	void *end = (void *)((unsigned long)start + size);
> -	return ptr > end || ptr < start;
> -}
> -
> -/*
> - * Elf hash, see format specification.
> - */
> -static unsigned long elf_hash(const unsigned char *name)
> -{
> -	unsigned long h = 0, g;
> -
> -	while (*name) {
> -		h = (h << 4) + *name++;
> -		g = h & 0xf0000000ul;
> -		if (g)
> -			h ^= g >> 24;
> -		h &= ~g;
> -	}
> -	return h;
> -}
> -
> -int vdso_fill_symtable(char *mem, size_t size, struct vdso_symtable *t)
> -{
> -	Elf64_Phdr *dynamic = NULL, *load = NULL;
> -	Elf64_Ehdr *ehdr = (void *)mem;
> -	Elf64_Dyn *dyn_strtab = NULL;
> -	Elf64_Dyn *dyn_symtab = NULL;
> -	Elf64_Dyn *dyn_strsz = NULL;
> -	Elf64_Dyn *dyn_syment = NULL;
> -	Elf64_Dyn *dyn_hash = NULL;
> -	Elf64_Word *hash = NULL;
> -	Elf64_Phdr *phdr;
> -	Elf64_Dyn *d;
> -
> -	Elf64_Word *bucket, *chain;
> -	Elf64_Word nbucket, nchain;
> -
> -	/*
> -	 * See Elf specification for this magic values.
> -	 */
> -	const char elf_ident[] = {
> -		0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00,
> -		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> -	};
> -
> -	const char *vdso_symbols[VDSO_SYMBOL_MAX] = {
> -		[VDSO_SYMBOL_CLOCK_GETRES]	= VDSO_SYMBOL_CLOCK_GETRES_NAME,
> -		[VDSO_SYMBOL_CLOCK_GETTIME]	= VDSO_SYMBOL_CLOCK_GETTIME_NAME,
> -		[VDSO_SYMBOL_GETTIMEOFDAY]	= VDSO_SYMBOL_GETTIMEOFDAY_NAME,
> -		[VDSO_SYMBOL_RT_SIGRETURN]	= VDSO_SYMBOL_RT_SIGRETURN_NAME,
> -	};

I need to debug further, but I think the code that replaced this is somehow
not properly position independent when I build for AArch64 and run. I'm
getting a segfault. The faulting address (for example 0x000055d8) is
vdso_symbols[0].

Some corresponding debug output I added:

pie: vdso: pc = 0x13b58
pie: vdso: vdso_symbols = 0x146e8
pie: vdso: vdso_symbols[0] = 0x55d8

I'll keep investigating, but any suggested anyone has would be appreciated.

I see this with both 4k and 64k pages (4k version above).

Thanks,
Christopher Covington

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