[v10,12/50] x86/sev: Invalidate pages from the direct map when adding them to the RMP table

Commit Message

Michael Roth Oct. 16, 2023, 1:27 p.m. UTC

From: Brijesh Singh <[e-mail]>

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-check 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 invalidate state so that pages cannot be used in the direct-map after
they are added the RMP table, and restored to their default valid
permission after the pages are removed from the RMP table.

Co-developed-by: Ashish Kalra <[e-mail]>
Signed-off-by: Ashish Kalra <[e-mail]>
Signed-off-by: Brijesh Singh <[e-mail]>
---
 arch/x86/virt/svm/sev.c | 62 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

Comments

Borislav Petkov Nov. 24, 2023, 2:20 p.m. UTC | #1

On Mon, Oct 16, 2023 at 08:27:41AM -0500, Michael Roth wrote:
> From: Brijesh Singh <[e-mail]>
> 
> 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-check 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 invalidate state so that pages cannot be used in the direct-map after
> they are added the RMP table, and restored to their default valid
> permission after the pages are removed from the RMP table.

Brijesh's SOB comes

<--- here,

then Ashish's two tags.

Please audit your whole set for such inconsistencies.

> @@ -404,6 +440,21 @@ static int rmpupdate(u64 pfn, struct rmp_state *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.

Here I'm missing the explanation *why* the pages need to be unmapped
from the direct map.

What happens if not?

> +	 */
> +	if (val->assigned) {
> +		if (invalidate_direct_map(pfn, npages)) {
> +			pr_err("Failed to unmap %d pages at pfn 0x%llx from the direct_map\n",
> +			       npages, pfn);

invalidate_direct_map() already dumps an error message - no need to do
that here too.

> +			return -EFAULT;
> +		}
> +	}
> +
>  	do {
>  		/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
>  		asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
> @@ -422,6 +473,17 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
>  		return -EFAULT;
>  	}
>  
> +	/*
> +	 * Restore the direct map after the page is removed from the RMP table.
> +	 */
> +	if (!val->assigned) {
> +		if (restore_direct_map(pfn, npages)) {
> +			pr_err("Failed to map %d pages at pfn 0x%llx into the direct_map\n",
> +			       npages, pfn);

Ditto.

Patch

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 24a695af13a5..bf9b97046e05 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -395,6 +395,42 @@  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)
+			break;
+	}
+
+	if (ret)
+		pr_warn("Failed to restore direct map for pfn 0x%llx, ret: %d\n",
+			pfn + i, ret);
+
+	return ret;
+}
+
+static int invalidate_direct_map(u64 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)
+			break;
+	}
+
+	if (ret) {
+		pr_warn("Failed to invalidate direct map for pfn 0x%llx, ret: %d\n",
+			pfn + i, ret);
+		restore_direct_map(pfn, i);
+	}
+
+	return ret;
+}
+
 static int rmpupdate(u64 pfn, struct rmp_state *val)
 {
 	unsigned long paddr = pfn << PAGE_SHIFT;
@@ -404,6 +440,21 @@  static int rmpupdate(u64 pfn, struct rmp_state *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 (invalidate_direct_map(pfn, npages)) {
+			pr_err("Failed to unmap %d pages at pfn 0x%llx from the direct_map\n",
+			       npages, pfn);
+			return -EFAULT;
+		}
+	}
+
 	do {
 		/* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
 		asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
@@ -422,6 +473,17 @@  static int rmpupdate(u64 pfn, struct rmp_state *val)
 		return -EFAULT;
 	}
 
+	/*
+	 * Restore the direct map after the page is removed from the RMP table.
+	 */
+	if (!val->assigned) {
+		if (restore_direct_map(pfn, npages)) {
+			pr_err("Failed to map %d pages at pfn 0x%llx into the direct_map\n",
+			       npages, pfn);
+			return -EFAULT;
+		}
+	}
+
 	return 0;
 }