[PATCH] xen/setup: add paranoid index check and warning

[Martin Kelly]

In a call to set_phys_range_identity, i-1 is used without checking that
i is non-zero. Although unlikely, a bug in the code before it could
cause the value to be 0, leading to erroneous behavior. This patch adds
a check against 0 value and a corresponding warning.

Signed-off-by: Martin Kelly <martkell@xxxxxxxxxx>
---
 arch/x86/xen/setup.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index af72161..26e39af 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -671,7 +671,10 @@ char * __init xen_memory_setup(void)
 	 * PFNs above MAX_P2M_PFN are considered identity mapped as
 	 * well.
 	 */
-	set_phys_range_identity(map[i-1].addr / PAGE_SIZE, ~0ul);
+	if (i > 0)
+		set_phys_range_identity(map[i-1].addr / PAGE_SIZE, ~0ul);
+	else
+		WARN(1, "Something went wrong clamping memory to a factor of EXTRA_MEM_RATIO!");
 
 	/*
 	 * In domU, the ISA region is normal, usable memory, but we
-- 
2.1.1

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