KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 198 insertions, 0 deletions

diff --git a/scripts/elf-parse.c b/scripts/elf-parse.c
new file mode 100644
index 000000000..99869ff91
--- /dev/null
+++ b/scripts/elf-parse.c
@@ -0,0 +1,198 @@
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "elf-parse.h"
+
+struct elf_funcs elf_parser;
+
+/*
+ * Get the whole file as a programming convenience in order to avoid
+ * malloc+lseek+read+free of many pieces.  If successful, then mmap
+ * avoids copying unused pieces; else just read the whole file.
+ * Open for both read and write.
+ */
+static void *map_file(char const *fname, size_t *size)
+{
+	int fd;
+	struct stat sb;
+	void *addr = NULL;
+
+	fd = open(fname, O_RDWR);
+	if (fd < 0) {
+		perror(fname);
+		return NULL;
+	}
+	if (fstat(fd, &sb) < 0) {
+		perror(fname);
+		goto out;
+	}
+	if (!S_ISREG(sb.st_mode)) {
+		fprintf(stderr, "not a regular file: %s\n", fname);
+		goto out;
+	}
+
+	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (addr == MAP_FAILED) {
+		fprintf(stderr, "Could not mmap file: %s\n", fname);
+		goto out;
+	}
+
+	*size = sb.st_size;
+
+out:
+	close(fd);
+	return addr;
+}
+
+static int elf_parse(const char *fname, void *addr, uint32_t types)
+{
+	Elf_Ehdr *ehdr = addr;
+	uint16_t type;
+
+	switch (ehdr->e32.e_ident[EI_DATA]) {
+	case ELFDATA2LSB:
+		elf_parser.r	= rle;
+		elf_parser.r2	= r2le;
+		elf_parser.r8	= r8le;
+		elf_parser.w	= wle;
+		elf_parser.w8	= w8le;
+		break;
+	case ELFDATA2MSB:
+		elf_parser.r	= rbe;
+		elf_parser.r2	= r2be;
+		elf_parser.r8	= r8be;
+		elf_parser.w	= wbe;
+		elf_parser.w8	= w8be;
+		break;
+	default:
+		fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
+			ehdr->e32.e_ident[EI_DATA], fname);
+		return -1;
+	}
+
+	if (memcmp(ELFMAG, ehdr->e32.e_ident, SELFMAG) != 0 ||
+	    ehdr->e32.e_ident[EI_VERSION] != EV_CURRENT) {
+		fprintf(stderr, "unrecognized ELF file %s\n", fname);
+		return -1;
+	}
+
+	type = elf_parser.r2(&ehdr->e32.e_type);
+	if (!((1 << type) & types)) {
+		fprintf(stderr, "Invalid ELF type file %s\n", fname);
+		return -1;
+	}
+
+	switch (ehdr->e32.e_ident[EI_CLASS]) {
+	case ELFCLASS32: {
+		elf_parser.ehdr_shoff		= ehdr32_shoff;
+		elf_parser.ehdr_shentsize	= ehdr32_shentsize;
+		elf_parser.ehdr_shstrndx	= ehdr32_shstrndx;
+		elf_parser.ehdr_shnum		= ehdr32_shnum;
+		elf_parser.shdr_addr		= shdr32_addr;
+		elf_parser.shdr_offset		= shdr32_offset;
+		elf_parser.shdr_link		= shdr32_link;
+		elf_parser.shdr_size		= shdr32_size;
+		elf_parser.shdr_name		= shdr32_name;
+		elf_parser.shdr_type		= shdr32_type;
+		elf_parser.shdr_entsize		= shdr32_entsize;
+		elf_parser.sym_type		= sym32_type;
+		elf_parser.sym_name		= sym32_name;
+		elf_parser.sym_value		= sym32_value;
+		elf_parser.sym_shndx		= sym32_shndx;
+		elf_parser.rela_offset		= rela32_offset;
+		elf_parser.rela_info		= rela32_info;
+		elf_parser.rela_addend		= rela32_addend;
+		elf_parser.rela_write_addend	= rela32_write_addend;
+
+		if (elf_parser.r2(&ehdr->e32.e_ehsize) != sizeof(Elf32_Ehdr) ||
+		    elf_parser.r2(&ehdr->e32.e_shentsize) != sizeof(Elf32_Shdr)) {
+			fprintf(stderr,
+				"unrecognized ET_EXEC/ET_DYN file: %s\n", fname);
+			return -1;
+		}
+
+		}
+		break;
+	case ELFCLASS64: {
+		elf_parser.ehdr_shoff		= ehdr64_shoff;
+		elf_parser.ehdr_shentsize		= ehdr64_shentsize;
+		elf_parser.ehdr_shstrndx		= ehdr64_shstrndx;
+		elf_parser.ehdr_shnum		= ehdr64_shnum;
+		elf_parser.shdr_addr		= shdr64_addr;
+		elf_parser.shdr_offset		= shdr64_offset;
+		elf_parser.shdr_link		= shdr64_link;
+		elf_parser.shdr_size		= shdr64_size;
+		elf_parser.shdr_name		= shdr64_name;
+		elf_parser.shdr_type		= shdr64_type;
+		elf_parser.shdr_entsize		= shdr64_entsize;
+		elf_parser.sym_type		= sym64_type;
+		elf_parser.sym_name		= sym64_name;
+		elf_parser.sym_value		= sym64_value;
+		elf_parser.sym_shndx		= sym64_shndx;
+		elf_parser.rela_offset		= rela64_offset;
+		elf_parser.rela_info		= rela64_info;
+		elf_parser.rela_addend		= rela64_addend;
+		elf_parser.rela_write_addend	= rela64_write_addend;
+
+		if (elf_parser.r2(&ehdr->e64.e_ehsize) != sizeof(Elf64_Ehdr) ||
+		    elf_parser.r2(&ehdr->e64.e_shentsize) != sizeof(Elf64_Shdr)) {
+			fprintf(stderr,
+				"unrecognized ET_EXEC/ET_DYN file: %s\n",
+				fname);
+			return -1;
+		}
+
+		}
+		break;
+	default:
+		fprintf(stderr, "unrecognized ELF class %d %s\n",
+			ehdr->e32.e_ident[EI_CLASS], fname);
+		return -1;
+	}
+	return 0;
+}
+
+int elf_map_machine(void *addr)
+{
+	Elf_Ehdr *ehdr = addr;
+
+	return elf_parser.r2(&ehdr->e32.e_machine);
+}
+
+int elf_map_long_size(void *addr)
+{
+	Elf_Ehdr *ehdr = addr;
+
+	return ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8;
+}
+
+void *elf_map(char const *fname, size_t *size, uint32_t types)
+{
+	void *addr;
+	int ret;
+
+	addr = map_file(fname, size);
+	if (!addr)
+		return NULL;
+
+	ret = elf_parse(fname, addr, types);
+	if (ret < 0) {
+		elf_unmap(addr, *size);
+		return NULL;
+	}
+
+	return addr;
+}
+
+void elf_unmap(void *addr, size_t size)
+{
+	munmap(addr, size);
+}