linux-kernel - [PATCH v3 21/21] x86/kaslr: Add a check that the random address is in range

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Date:   Tue, 28 Jul 2020 18:57:22 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Kees Cook <keescook@...omium.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH v3 21/21] x86/kaslr: Add a check that the random address is in range

Check in find_random_phys_addr that the chosen address is inside the
range that was required.

Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 arch/x86/boot/compressed/kaslr.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 38ecbf2e61c5..903ccdca0551 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -802,6 +802,8 @@ static void process_e820_entries(unsigned long minimum,
 static unsigned long find_random_phys_addr(unsigned long minimum,
 					   unsigned long image_size)
 {
+	u64 phys_addr;
+
 	/* Bail out early if it's impossible to succeed. */
 	if (minimum + image_size > mem_limit)
 		return 0;
@@ -815,7 +817,15 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
 	if (!process_efi_entries(minimum, image_size))
 		process_e820_entries(minimum, image_size);
 
-	return slots_fetch_random();
+	phys_addr = slots_fetch_random();
+
+	/* Perform a final check to make sure the address is in range. */
+	if (phys_addr < minimum || phys_addr + image_size > mem_limit) {
+		warn("Invalid physical address chosen!\n");
+		return 0;
+	}
+
+	return (unsigned long)phys_addr;
 }
 
 static unsigned long find_random_virt_addr(unsigned long minimum,
-- 
2.26.2