In the past it used to point to 'sgdt' (native_store_gdt)
operation which is a non-privileged operation. This resulted
in the value of 'struct desc_ptr' pointing to an bogus address
0xffff820000000000, instead of the GDT table that Linux thinks
it is using. The end result is that doing:
store_gdt(&desc);
load_gdt(&desc);
would blow up b/c xen_load_gdt would try to parse the GDT contents
(desc) and de-reference an bogus virtual address.
With this patch we are providing the last written address and size
of the GDT.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
arch/x86/xen/enlighten.c | 16 +++++++++++++++-
1 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index f29d6d6..4a65138 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -471,6 +471,8 @@ static void xen_set_ldt(const void *addr, unsigned entries)
xen_mc_issue(PARAVIRT_LAZY_CPU);
}
+static DEFINE_PER_CPU(struct desc_ptr, gdt_desc);
+
static void xen_load_gdt(const struct desc_ptr *dtr)
{
unsigned long va = dtr->address;
@@ -478,6 +480,7 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
unsigned pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
unsigned long frames[pages];
int f;
+ struct desc_ptr *shadow;
/*
* A GDT can be up to 64k in size, which corresponds to 8192
@@ -515,8 +518,19 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
BUG();
+
+ shadow = &__get_cpu_var(gdt_desc);
+ shadow->address = dtr->address;
+ shadow->size = size;
}
+static void xen_store_gdt(struct desc_ptr *dtr)
+{
+ const struct desc_ptr *desc = &__get_cpu_var(gdt_desc);
+
+ dtr->address = desc->address;
+ dtr->size = desc->size;
+}
/*
* load_gdt for early boot, when the gdt is only mapped once
*/
@@ -1205,7 +1219,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
.alloc_ldt = xen_alloc_ldt,
.free_ldt = xen_free_ldt,
- .store_gdt = native_store_gdt,
+ .store_gdt = xen_store_gdt,
.store_idt = xen_store_idt,
.store_tr = xen_store_tr,
--
1.7.7.6
--
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