On 2/6/20 5:09 AM, Christian Borntraeger wrote:
On 05.02.20 19:21, Jason J. Herne wrote:
This fixes vfio-ccw when booting non-Linux operating systems. Without this
struct being packed, a few extra bytes of low core memory get overwritten when
we assign a value to memory address 0 in jump_to_IPL_2. This is enough to
cause some non-Linux OSes of fail when booting.
The problem was introduced by:
5c6f0d5f46a77d77 "pc-bios/s390x: Fix reset psw mask".
The fix is to pack the struct thereby removing the 4 bytes of padding that get
added at the end, likely to allow an array of these structs to naturally align
on an 8-byte boundary.
Fixes: 5c6f0d5f46a7 ("pc-bios/s390x: Fix reset psw mask")
CC: Janosch Frank <fran...@linux.ibm.com>
Signed-off-by: Jason J. Herne <jjhe...@linux.ibm.com>
---
pc-bios/s390-ccw/jump2ipl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index da13c43cc0..1e9eaa037f 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -18,7 +18,7 @@
typedef struct ResetInfo {
uint64_t ipl_psw;
uint32_t ipl_continue;
-} ResetInfo;
+} __attribute__((packed)) ResetInfo;
static ResetInfo save;
Just looked into that.
We do save the old content in "save" and restore the old memory content.
static void jump_to_IPL_2(void)
{
ResetInfo *current = 0;
void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue;
--->*current = save;
ipl(); /* should not return */
}
void jump_to_IPL_code(uint64_t address)
{
/* store the subsystem information _after_ the bootmap was loaded */
write_subsystem_identification();
/* prevent unknown IPL types in the guest */
if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
iplb.pbt = S390_IPL_TYPE_CCW;
set_iplb(&iplb);
}
/*
* The IPL PSW is at address 0. We also must not overwrite the
* content of non-BIOS memory after we loaded the guest, so we
* save the original content and restore it in jump_to_IPL_2.
*/
ResetInfo *current = 0;
--->save = *current;
does something like
diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index da13c43cc0..8839226803 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -18,6 +18,7 @@
typedef struct ResetInfo {
uint64_t ipl_psw;
uint32_t ipl_continue;
+ uint32_t pad;
} ResetInfo;
static ResetInfo save;
also work? If yes, both variants are valid. Either packed or explicit padding.
I don't believe this will work. I think the problem is that we're overwriting too much
memory when we cast address 0 as a ResetInfo and then overwrite it (*current = save). I
think we need the struct to be sized at 12-bytes instead of 16.
--
-- Jason J. Herne (jjhe...@linux.ibm.com)
