From 494f881f279be3e37b5ddb44e76ec1bcad70a217 Mon Sep 17 00:00:00 2001
From: Stefan Kalkowski <stefan.kalkowski@genode-labs.com>
Date: Wed, 16 Feb 2022 11:33:51 +0100
Subject: [PATCH] core: don't use frame 0 for managing_system pd

When a PD owns the right to ask for a RAM dataspace's `dma_addr` it is
concurrently constrained to use allocations of a specific physical RAM area.
This commit further limits this area by removing RAM page frame zero.
Otherwise the return value of `dma_addr` for such a dataspace would be
erroneously interpreted as a fault, because zero is currently the error
return value of `dma_addr`.

Fix genodelabs/genode#4428
---
 repos/base/src/core/include/pd_root.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/repos/base/src/core/include/pd_root.h b/repos/base/src/core/include/pd_root.h
index 5bc6ec5933..5e92307a05 100644
--- a/repos/base/src/core/include/pd_root.h
+++ b/repos/base/src/core/include/pd_root.h
@@ -47,7 +47,11 @@ class Genode::Pd_root : public Genode::Root_component<Genode::Pd_session_compone
 			if (_managing_system(args) == Pd_session_component::Managing_system::DENIED)
 				return Ram_dataspace_factory::any_phys_range();
 
-			addr_t const start = 0;
+			/*
+			 * Leave out first page because currently return value zero
+			 * for dma_addr is recognized as a fault
+			 */
+			addr_t const start = 0x1000;
 			addr_t const end   = (sizeof(long) == 4) /* 32bit arch ? */
 			                   ? 0xbfffffffUL : 0xffffffffUL;