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s390/extmem: return correct segment type in __segment_load() 

Commit f05f62d042 ("s390/vmem: get rid of memory segment list")
reshuffled the call to vmem_add_mapping() in __segment_load(), which now
overwrites rc after it was set to contain the segment type code.

As result, __segment_load() will now always return 0 on success, which
corresponds to the segment type code SEG_TYPE_SW, i.e. a writeable
segment. This results in a kernel crash when loading a read-only segment
as dcssblk block device, and trying to write to it.

Instead of reshuffling code again, make sure to return the segment type
on success, and also describe this rather delicate and unexpected logic
in the function comment. Also initialize new segtype variable with
invalid value, to prevent possible future confusion.

Fixes: f05f62d042 ("s390/vmem: get rid of memory segment list")
Cc: <stable@vger.kernel.org> # 5.9+
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Gerald Schaefer 2023-02-27 20:03:00 +01:00 committed by Heiko Carstens
parent 9b5c37bbf6
commit 8c42dd78df
1 changed files with 7 additions and 5 deletions
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12
arch/s390/mm/extmem.c
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@ -289,15 +289,17 @@ segment_overlaps_others (struct dcss_segment *seg)
/*
* real segment loading function, called from segment_load
* Must return either an error code < 0, or the segment type code >= 0
*/
static int
__segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long *end)
{
unsigned long start_addr, end_addr, dummy;
struct dcss_segment *seg;
int rc, diag_cc;
int rc, diag_cc, segtype;
start_addr = end_addr = 0;
segtype = -1;
seg = kmalloc(sizeof(*seg), GFP_KERNEL | GFP_DMA);
if (seg == NULL) {
rc = -ENOMEM;
@ -326,9 +328,9 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
seg->res_name[8] = '\0';
strlcat(seg->res_name, " (DCSS)", sizeof(seg->res_name));
seg->res->name = seg->res_name;
rc = seg->vm_segtype;
if (rc == SEG_TYPE_SC ||
((rc == SEG_TYPE_SR || rc == SEG_TYPE_ER) && !do_nonshared))
segtype = seg->vm_segtype;
if (segtype == SEG_TYPE_SC ||
((segtype == SEG_TYPE_SR || segtype == SEG_TYPE_ER) && !do_nonshared))
seg->res->flags |= IORESOURCE_READONLY;
/* Check for overlapping resources before adding the mapping. */
@ -386,7 +388,7 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
out_free:
kfree(seg);
out:
return rc;
return rc < 0 ? rc : segtype;
}
/*