[Xen-devel] [PATCH v5 1/4] livepatch/docs: Document .bss not being cleared, and .data potentially having changed values

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

. since the load time.

In summary we clear the .bss only during upload time. Subsequent
apply/revert/apply can change the .bss values - meaning that the
.bss values are not guaranteed to be zero - in fact they can be
anything!

And the .data can also be in various states.

Suggested-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

---
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>

v5: New submission
---
 docs/misc/livepatch.markdown | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/docs/misc/livepatch.markdown b/docs/misc/livepatch.markdown
index 89c1050..07be0af 100644
--- a/docs/misc/livepatch.markdown
+++ b/docs/misc/livepatch.markdown
@@ -875,6 +875,12 @@ section and the new function will reference the new string 
in the new
 
 This is implemented in the Xen Project hypervisor.
 
+Note that the .bss section is only cleared when the ELF payload is uploaded.
+Subsequent apply/revert/apply operation do no clear the .bss (or reset the
+.data to what it was when loaded). Hence it is the responsibility of the
+creator of the payload to reset these values to known good state if they
+depend on them having certain values at apply/revert states.
+
 ### Security
 
 Only the privileged domain should be allowed to do this operation.
-- 
2.4.11


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