Hi Konrad,
On 25/08/16 14:37, Konrad Rzeszutek Wilk wrote:
With livepatching the alternatives that should be patched are
outside the Xen hypervisor _start -> _end. As such having
to use an alternative VA is not neccessary. In fact we
s/neccessary/necessary/
can use the ones that the caller provided us with.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
---
Cc: Stefano Stabellini <sstabell...@kernel.org>
Cc: Julien Grall <julien.gr...@arm.com>
v2: First version
---
xen/arch/arm/alternative.c | 40 +++++++++++++++++++++++++---------------
1 file changed, 25 insertions(+), 15 deletions(-)
diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c
index aba06db..90a857a 100644
--- a/xen/arch/arm/alternative.c
+++ b/xen/arch/arm/alternative.c
@@ -94,24 +94,30 @@ static int __apply_alternatives(const struct alt_region
*region)
{
const struct alt_instr *alt;
const u32 *origptr, *replptr;
- u32 *writeptr, *writemap;
+ u32 *writeptr, *writemap = NULL;
mfn_t text_mfn = _mfn(virt_to_mfn(_stext));
unsigned int text_order = get_order_from_bytes(_end - _start);
- printk(XENLOG_INFO "alternatives: Patching kernel code\n");
-
- /*
- * The text section is read-only. So re-map Xen to be able to patch
- * the code.
- */
- writemap = __vmap(&text_mfn, 1 << text_order, 1, 1, PAGE_HYPERVISOR,
- VMAP_DEFAULT);
- if ( !writemap )
+ if ( region->begin >= __alt_instructions &&
+ region->end <= __alt_instructions_end )
I think this is quite fragile because __alt_instructions is part of the
init section. So after runtime, those regions could be reallocated for
other purposes.
I thought a bit more about the issue, each alt_instr contains a relative
offset. So it would be possible to re-map the region in
__apply_alternatives_multi_stop and passed the re-map the region to
__apply_alternatives.
Furthermore, I think it is safe to mandate apply_alternatives to work
only read-write region.
So we could simplify the hacky code I wrote to workaround the Write
permissions implies execute-never.
Let me try to write a patch to see if my solution works.
Regards,
--
Julien Grall
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