[PATCH Part2 v5 06/45] x86/sev: Invalid pages from direct map when adding it to RMP table

Brijesh Singh
2021-08-20T16:00:05Z

The integrity guarantee of SEV-SNP is enforced through the RMP table.
The RMP is used with standard x86 and IOMMU page tables to enforce memory
restrictions and page access rights. The RMP check is enforced as soon as
SEV-SNP is enabled globally in the system. When hardware encounters an
RMP checks failure, it raises a page-fault exception.

The rmp_make_private() and rmp_make_shared() helpers are used to add
or remove the pages from the RMP table. Improve the rmp_make_private() to
invalid state so that pages cannot be used in the direct-map after its
added in the RMP table, and restore to its default valid permission after
the pages are removed from the RMP table.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/kernel/sev.c | 61 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 60 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 8627c49666c9..bad41deb8335 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2441,10 +2441,42 @@ int psmash(u64 pfn)
}
EXPORT_SYMBOL_GPL(psmash);

+static int restore_direct_map(u64 pfn, int npages)
+{
+ int i, ret = 0;
+
+ for (i = 0; i < npages; i++) {
+ ret = set_direct_map_default_noflush(pfn_to_page(pfn + i));
+ if (ret)
+ goto cleanup;
+ }
+
+cleanup:
+ WARN(ret > 0, "Failed to restore direct map for pfn 0x%llx\n", pfn + i);
+ return ret;
+}
+
+static int invalid_direct_map(unsigned long pfn, int npages)
+{
+ int i, ret = 0;
+
+ for (i = 0; i < npages; i++) {
+ ret = set_direct_map_invalid_noflush(pfn_to_page(pfn + i));
+ if (ret)
+ goto cleanup;
+ }
+
+ return 0;
+
+cleanup:
+ restore_direct_map(pfn, i);
+ return ret;
+}
+
static int rmpupdate(u64 pfn, struct rmpupdate *val)
{
unsigned long paddr = pfn << PAGE_SHIFT;
- int ret;
+ int ret, level, npages;

if (!pfn_valid(pfn))
return -EINVAL;
@@ -2452,11 +2484,38 @@ static int rmpupdate(u64 pfn, struct rmpupdate *val)
if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
return -ENXIO;

+ level = RMP_TO_X86_PG_LEVEL(val->pagesize);
+ npages = page_level_size(level) / PAGE_SIZE;
+
+ /*
+ * If page is getting assigned in the RMP table then unmap it from the
+ * direct map.
+ */
+ if (val->assigned) {
+ if (invalid_direct_map(pfn, npages)) {
+ pr_err("Failed to unmap pfn 0x%llx pages %d from direct_map\n",
+ pfn, npages);
+ return -EFAULT;
+ }
+ }
+
/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
: "=a"(ret)
: "a"(paddr), "c"((unsigned long)val)
: "memory", "cc");
+
+ /*
+ * Restore the direct map after the page is removed from the RMP table.
+ */
+ if (!ret && !val->assigned) {
+ if (restore_direct_map(pfn, npages)) {
+ pr_err("Failed to map pfn 0x%llx pages %d in direct_map\n",
+ pfn, npages);
+ return -EFAULT;
+ }
+ }
+
return ret;
}

--
2.17.1