[PATCH 6.19 698/844] ima: verify the previous kernel's IMA buffer lies in addressable RAM

[Sasha Levin]

From: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>

[ Upstream commit 10d1c75ed4382a8e79874379caa2ead8952734f9 ]

Patch series "Address page fault in ima_restore_measurement_list()", v3.

When the second-stage kernel is booted via kexec with a limiting command
line such as "mem=<size>" we observe a pafe fault that happens.

    BUG: unable to handle page fault for address: ffff97793ff47000
    RIP: ima_restore_measurement_list+0xdc/0x45a
    #PF: error_code(0x0000)  not-present page

This happens on x86_64 only, as this is already fixed in aarch64 in
commit: cbf9c4b9617b ("of: check previous kernel's ima-kexec-buffer
against memory bounds")

This patch (of 3):

When the second-stage kernel is booted with a limiting command line (e.g.
"mem=<size>"), the IMA measurement buffer handed over from the previous
kernel may fall outside the addressable RAM of the new kernel.  Accessing
such a buffer can fault during early restore.

Introduce a small generic helper, ima_validate_range(), which verifies
that a physical [start, end] range for the previous-kernel IMA buffer lies
within addressable memory:
	- On x86, use pfn_range_is_mapped().
	- On OF based architectures, use page_is_ram().

Link: https://lkml.kernel.org/r/20251231061609.907170-1-harshit.m.mogalapalli@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20251231061609.907170-2-harshit.m.mogalapalli@xxxxxxxxxx
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Cc: Alexander Graf <graf@xxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Borislav Betkov <bp@xxxxxxxxx>
Cc: guoweikang <guoweikang.kernel@xxxxxxxxx>
Cc: Henry Willard <henry.willard@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jiri Bohac <jbohac@xxxxxxx>
Cc: Joel Granados <joel.granados@xxxxxxxxxx>
Cc: Jonathan McDowell <noodles@xxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Paul Webb <paul.x.webb@xxxxxxxxxx>
Cc: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Cc: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Cc: Thomas Gleinxer <tglx@xxxxxxxxxxxxx>
Cc: Yifei Liu <yifei.l.liu@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/ima.h                |  1 +
 security/integrity/ima/ima_kexec.c | 35 ++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 8e29cb4e6a01d..abf8923f8fc51 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -69,6 +69,7 @@ static inline int ima_measure_critical_data(const char *event_label,
 #ifdef CONFIG_HAVE_IMA_KEXEC
 int __init ima_free_kexec_buffer(void);
 int __init ima_get_kexec_buffer(void **addr, size_t *size);
+int ima_validate_range(phys_addr_t phys, size_t size);
 #endif
 
 #ifdef CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 5beb69edd12fd..36a34c54de58b 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -12,6 +12,8 @@
 #include <linux/kexec.h>
 #include <linux/of.h>
 #include <linux/ima.h>
+#include <linux/mm.h>
+#include <linux/overflow.h>
 #include <linux/reboot.h>
 #include <asm/page.h>
 #include "ima.h"
@@ -294,3 +296,36 @@ void __init ima_load_kexec_buffer(void)
 		pr_debug("Error restoring the measurement list: %d\n", rc);
 	}
 }
+
+/*
+ * ima_validate_range - verify a physical buffer lies in addressable RAM
+ * @phys: physical start address of the buffer from previous kernel
+ * @size: size of the buffer
+ *
+ * On success return 0. On failure returns -EINVAL so callers can skip
+ * restoring.
+ */
+int ima_validate_range(phys_addr_t phys, size_t size)
+{
+	unsigned long start_pfn, end_pfn;
+	phys_addr_t end_phys;
+
+	if (check_add_overflow(phys, (phys_addr_t)size - 1, &end_phys))
+		return -EINVAL;
+
+	start_pfn = PHYS_PFN(phys);
+	end_pfn = PHYS_PFN(end_phys);
+
+#ifdef CONFIG_X86
+	if (!pfn_range_is_mapped(start_pfn, end_pfn))
+#else
+	if (!page_is_ram(start_pfn) || !page_is_ram(end_pfn))
+#endif
+	{
+		pr_warn("IMA: previous kernel measurement buffer %pa (size 0x%zx) lies outside available memory\n",
+			&phys, size);
+		return -EINVAL;
+	}
+
+	return 0;
+}
-- 
2.51.0