linux-kernel - [PATCH 4/4] riscv: libstub: Implement KASLR by using generic functions

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Message-Id: <20230215145113.465558-5-alexghiti@rivosinc.com>
Date:   Wed, 15 Feb 2023 15:51:13 +0100
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Ard Biesheuvel <ardb@...nel.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-efi@...r.kernel.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH 4/4] riscv: libstub: Implement KASLR by using generic functions

We can now use arm64 functions to handle the move of the kernel physical
mapping: if KASLR is enabled, we will try to get a random seed from the
firmware, if not possible, the kernel will be moved to a location that
suits its alignment constraints.

Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
---
 drivers/firmware/efi/libstub/riscv-stub.c | 27 ++++++++---------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/drivers/firmware/efi/libstub/riscv-stub.c b/drivers/firmware/efi/libstub/riscv-stub.c
index 145c9f0ba217..0c3c4a13afa1 100644
--- a/drivers/firmware/efi/libstub/riscv-stub.c
+++ b/drivers/firmware/efi/libstub/riscv-stub.c
@@ -30,32 +30,23 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 efi_loaded_image_t *image,
 				 efi_handle_t image_handle)
 {
-	unsigned long kernel_size = 0;
-	unsigned long preferred_addr;
+	unsigned long kernel_size, kernel_memsize = 0;
 	efi_status_t status;
 
 	kernel_size = _edata - _start;
+	kernel_memsize = kernel_size + (_end - _edata);
 	*image_addr = (unsigned long)_start;
-	*image_size = kernel_size + (_end - _edata);
-
-	/*
-	 * RISC-V kernel maps PAGE_OFFSET virtual address to the same physical
-	 * address where kernel is booted. That's why kernel should boot from
-	 * as low as possible to avoid wastage of memory. Currently, dram_base
-	 * is occupied by the firmware. So the preferred address for kernel to
-	 * boot is next aligned address. If preferred address is not available,
-	 * relocate_kernel will fall back to efi_low_alloc_above to allocate
-	 * lowest possible memory region as long as the address and size meets
-	 * the alignment constraints.
-	 */
-	preferred_addr = EFI_KIMG_PREFERRED_ADDRESS;
-	status = efi_relocate_kernel(image_addr, kernel_size, *image_size,
-				     preferred_addr, efi_get_kimg_min_align(),
-				     0x0);
+	*image_size = kernel_memsize;
+	*reserve_size = *image_size;
 
+	status = efi_kaslr_relocate_kernel(image_addr,
+					   reserve_addr, reserve_size,
+					   kernel_size, kernel_memsize,
+					   efi_kaslr_get_phys_seed(image_handle));
 	if (status != EFI_SUCCESS) {
 		efi_err("Failed to relocate kernel\n");
 		*image_size = 0;
 	}
+
 	return status;
 }
-- 
2.37.2