[PATCH makedumpfile] Avoid false-positive mem_section validation with vmlinux

[Pingfan Liu]

On Wed, Apr 20, 2022 at 11:58:29PM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> Currently get_mem_section() validates if SYMBOL(mem_section) is the address
> of the mem_section array first.  But there was a report that the first
> validation wrongly returned TRUE with -x vmlinux and SPARSEMEM_EXTREME
> (4.15+) on s390x.  This leads to crash failing statup with the following
> seek error:
> 
>   crash: seek error: kernel virtual address: 67fffc2800  type: "memory section root table"
> 
> Skip the first validation when satisfying the conditions.
> 

I still prefer to your V1, which is discussed internally. In which, the
logic was made straight forward. And I suggest some slight change to
your V1, which folds "-x vmlinux" logic into is_sparsemem_extreme().

What about the following: (not tested yet, if it is good, I can test it)


diff --git a/makedumpfile.c b/makedumpfile.c
index a2f45c8..3ebe372 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -2240,11 +2240,18 @@ int
 is_sparsemem_extreme(void)
 {
 	if ((ARRAY_LENGTH(mem_section)
-	     == divideup(NR_MEM_SECTIONS(), _SECTIONS_PER_ROOT_EXTREME()))
-	    || (ARRAY_LENGTH(mem_section) == NOT_FOUND_STRUCTURE))
-		return TRUE;
-	else
+	     == divideup(NR_MEM_SECTIONS(), _SECTIONS_PER_ROOT_EXTREME())) {
+	     return TRUE;
+	} else if (info->name_vmlinux) {
+		unsigned long flag = 0;
+
+		if (get_symbol_type_name("mem_section", DWARF_INFO_GET_SYMBOL_TYPE,
+				NULL, &flag)
+		    && !(flag & TYPE_ARRAY))
+		        return TRUE;
+	} else {
 		return FALSE;
+	}
 }
 
 int
@@ -3704,28 +3711,24 @@ get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
 {
 	int ret = FALSE;
 	unsigned long *mem_sec = NULL;
+	unsigned long mem_section_ptr = SYMBOL(mem_section);
 
 	if ((mem_sec = malloc(mem_section_size)) == NULL) {
 		ERRMSG("Can't allocate memory for the mem_section. %s\n",
 		    strerror(errno));
 		return FALSE;
 	}
-	ret = validate_mem_section(mem_sec, SYMBOL(mem_section),
-				   mem_section_size, mem_maps, num_section);
-
-	if (!ret && is_sparsemem_extreme()) {
-		unsigned long mem_section_ptr;
 
+	if (is_sparsemem_extreme()) {
 		if (!readmem(VADDR, SYMBOL(mem_section), &mem_section_ptr,
 			     sizeof(mem_section_ptr)))
 			goto out;
+	}
 
-		ret = validate_mem_section(mem_sec, mem_section_ptr,
-				mem_section_size, mem_maps, num_section);
-
-		if (!ret)
+	ret = validate_mem_section(mem_sec, mem_section_ptr,
+		mem_section_size, mem_maps, num_section);
+	if (!ret)
 			ERRMSG("Could not validate mem_section.\n");
-	}
 out:
 	if (mem_sec != NULL)
 		free(mem_sec);
-- 

Thanks,

	Pingfan

> Reported-by: Dave Wysochanski <dwysocha at redhat.com>
> Signed-off-by: Kazuhito Hagio <k-hagio-ab at nec.com>
> ---
>  makedumpfile.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index a2f45c84cee3..65d1c7c2f02c 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -3698,6 +3698,22 @@ validate_mem_section(unsigned long *mem_sec,
>  	return ret;
>  }
>  
> +/*
> + * SYMBOL(mem_section) varies with the combination of memory model and
> + * its source:
> + *
> + * SPARSEMEM
> + *   vmcoreinfo: address of mem_section root array
> + *   -x vmlinux: address of mem_section root array
> + *
> + * SPARSEMEM_EXTREME v1
> + *   vmcoreinfo: address of mem_section root array
> + *   -x vmlinux: address of mem_section root array
> + *
> + * SPARSEMEM_EXTREME v2 (with 83e3c48729d9 and a0b1280368d1) 4.15+
> + *   vmcoreinfo: address of mem_section root array
> + *   -x vmlinux: address of pointer to mem_section root array
> + */
>  static int
>  get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
>  		unsigned int num_section)
> @@ -3710,12 +3726,27 @@ get_mem_section(unsigned int mem_section_size, unsigned long *mem_maps,
>  		    strerror(errno));
>  		return FALSE;
>  	}
> +
> +	/*
> +	 * There was a report that the first validation wrongly returned TRUE
> +	 * with -x vmlinux and SPARSEMEM_EXTREME v2 on s390x, so skip it.
> +	 * Howerver, leave the fallback validation as it is for the -i option.
> +	 */
> +	if (is_sparsemem_extreme() && info->name_vmlinux) {
> +		unsigned long flag = 0;
> +		if (get_symbol_type_name("mem_section", DWARF_INFO_GET_SYMBOL_TYPE,
> +					NULL, &flag)
> +		    && !(flag & TYPE_ARRAY))
> +			goto skip_1st_validation;
> +	}
> +
>  	ret = validate_mem_section(mem_sec, SYMBOL(mem_section),
>  				   mem_section_size, mem_maps, num_section);
>  
>  	if (!ret && is_sparsemem_extreme()) {
>  		unsigned long mem_section_ptr;
>  
> +skip_1st_validation:
>  		if (!readmem(VADDR, SYMBOL(mem_section), &mem_section_ptr,
>  			     sizeof(mem_section_ptr)))
>  			goto out;
> -- 
> 2.27.0
>