shim: add HSIStatus feature

hughsie asked me if I can make shim tell userland what kinds of accesses
are allowed to the heap, stack, and allocations on the running platform,
so that these could be reported up through fwupd's Host Security ID
program (see https://fwupd.github.io/libfwupdplugin/hsi.html ).

This adds a new config-only (i.e. not a UEFI variable) variable
generated during boot, "/sys/firmware/efi/mok-variables/HSIStatus",
which tells us those properties as well as if the EFI Memory Attribute
Protocol is present.

Signed-off-by: Peter Jones <pjones@redhat.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/mok.c b/mok.c
index 67a798a3..5c7f9a2b 100644
--- a/mok.c
+++ b/mok.c
@@ -34,6 +34,44 @@ static BOOLEAN check_var(CHAR16 *varname)
 		efi_status_;                                                        \
 	})
 
+static UINTN
+format_hsi_status(UINT8 *buf, size_t sz,
+		  struct mok_state_variable *msv UNUSED)
+{
+	const char heapx[] = "heap-is-executable: ";
+	const char stackx[] = "\nstack-is-executable: ";
+	const char row[] = "\nro-sections-are-writable: ";
+	const char hasmap[] = "\nhas-memory-attribute-protocol: ";
+	const char finale[] = "\n";
+	char *pos;
+
+	/*
+	 * sizeof includes the trailing NUL which is where our 0 or 1 value
+	 * fits
+	 */
+	UINTN ret = sizeof(heapx) + sizeof(stackx) +
+		    sizeof(row) + sizeof(hasmap) +
+		    sizeof(finale);
+
+	if (buf == 0 || sz < ret) {
+		return ret;
+	}
+
+	buf[0] = 0;
+	pos = (char *)buf;
+	pos = stpcpy(pos, heapx);
+	pos = stpcpy(pos, (hsi_status & SHIM_HSI_STATUS_HEAPX) ? "1" : "0");
+	pos = stpcpy(pos, stackx);
+	pos = stpcpy(pos, (hsi_status & SHIM_HSI_STATUS_STACKX) ? "1" : "0");
+	pos = stpcpy(pos, row);
+	pos = stpcpy(pos, (hsi_status & SHIM_HSI_STATUS_ROW) ? "1" : "0");
+	pos = stpcpy(pos, hasmap);
+	pos = stpcpy(pos, (hsi_status & SHIM_HSI_STATUS_HASMAP) ? "1" : "0");
+	stpcpy(pos, finale);
+
+	return ret;
+}
+
 /*
  * If the OS has set any of these variables we need to drop into MOK and
  * handle them appropriately
@@ -223,6 +261,14 @@ struct mok_state_variable mok_state_variable_data[] = {
 	 .pcr = 14,
 	 .state = &mok_policy,
 	},
+	{.name = L"HSIStatus",
+	 .name8 = "HSIStatus",
+	 .rtname = L"HSIStatus",
+	 .rtname8 = "HSIStatus",
+	 .guid = &SHIM_LOCK_GUID,
+	 .flags = MOK_VARIABLE_CONFIG_ONLY,
+	 .format = format_hsi_status,
+	},
 	{ NULL, }
 };
 size_t n_mok_state_variables = sizeof(mok_state_variable_data) / sizeof(mok_state_variable_data[0]);