Currently, kernel_uimage_probe() does not set info->zimage.start. As a result, it contains the default value (ie 0). This causes, kernel_zimage_place() to treat the binary (contained within uImage) as position independent executable. Thus, it loads it at an incorrect address.
The correct approach would be to read "uimage.ep" and set info->zimage.start. This will ensure that the binary is loaded at the correct address. Also, it checks that the load address and entry address are the same. The reason being we currently support non compressed images for uImage header. And as seen in uboot sources(image_decomp(), case IH_COMP_NONE), load address and entry address can be the same. This behavior is applicable for both arm and arm64 platforms. Earlier for arm32 and arm64 platforms, Xen was ignoring the entry point address set in the uImage header. With this commit, Xen will use the kernel entry point address as specified in the header. This makes the behavior of Xen consistent with uboot for uimage headers. Users who want to use Xen with statically partitioned domains, can provide the fixed non zero load address for the dom0/domU kernel. A deviation from uboot behaviour is that we consider load address == 0x0, to denote that the image supports position independent execution. This is to make the behavior consistent across uImage and zImage. Signed-off-by: Ayan Kumar Halder <ayan.kumar.hal...@amd.com> --- Changes from v1 :- 1. Added a check to ensure load address and entry address are the same. 2. Considered load address == 0x0 as position independent execution. 3. Ensured that the uImage header interpretation is consistent across arm32 and arm64. v2 :- 1. Mentioned the change in existing behavior in booting.txt. 2. Updated booting.txt with a new section to document "Booting Guests". docs/misc/arm/booting.txt | 21 +++++++++++++++++++++ xen/arch/arm/include/asm/kernel.h | 2 +- xen/arch/arm/kernel.c | 27 ++++++++++++++++++++++++++- 3 files changed, 48 insertions(+), 2 deletions(-) diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt index 3e0c03e065..01b12b49a5 100644 --- a/docs/misc/arm/booting.txt +++ b/docs/misc/arm/booting.txt @@ -23,6 +23,24 @@ The exceptions to this on 32-bit ARM are as follows: There are no exception on 64-bit ARM. +Booting Guests +-------------- + +Xen supports the legacy image protocol[3], zImage protocol for 32-bit ARM +Linux[1] and Image protocol defined for ARM64[2]. + +Earlier for legacy image protocol, Xen ignored the load address and entry +point specified in the header. This has now changed. + +Now, it loads the image at the load address provided in the header. +For now, it supports images where load address is same as entry point. + +A deviation from uboot is that, Xen treats "load address == 0x0" as +position independent execution. Thus, Xen will load such an image at an +address it considers appropriate. + +Users who want to use Xen with statically partitioned domains, can provide +the fixed non zero load address for the dom0/domU kernel. Firmware/bootloader requirements -------------------------------- @@ -39,3 +57,6 @@ Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/t [2] linux/Documentation/arm64/booting.rst Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.rst + +[3] legacy format header +Latest version: https://source.denx.de/u-boot/u-boot/-/blob/master/include/image.h#L315 diff --git a/xen/arch/arm/include/asm/kernel.h b/xen/arch/arm/include/asm/kernel.h index 5bb30c3f2f..4617cdc83b 100644 --- a/xen/arch/arm/include/asm/kernel.h +++ b/xen/arch/arm/include/asm/kernel.h @@ -72,7 +72,7 @@ struct kernel_info { #ifdef CONFIG_ARM_64 paddr_t text_offset; /* 64-bit Image only */ #endif - paddr_t start; /* 32-bit zImage only */ + paddr_t start; /* Must be 0 for 64-bit Image */ } zimage; }; }; diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c index 23b840ea9e..e9c18993ef 100644 --- a/xen/arch/arm/kernel.c +++ b/xen/arch/arm/kernel.c @@ -127,7 +127,7 @@ static paddr_t __init kernel_zimage_place(struct kernel_info *info) paddr_t load_addr; #ifdef CONFIG_ARM_64 - if ( info->type == DOMAIN_64BIT ) + if ( (info->type == DOMAIN_64BIT) && (info->zimage.start == 0) ) return info->mem.bank[0].start + info->zimage.text_offset; #endif @@ -223,6 +223,31 @@ static int __init kernel_uimage_probe(struct kernel_info *info, if ( len > size - sizeof(uimage) ) return -EINVAL; + info->zimage.start = be32_to_cpu(uimage.ep); + + /* + * Currently, we support uImage headers for uncompressed images only. + * Thus, it is valid for the load address and start address to be the + * same. This is consistent with the uboot behavior (Refer + * "case IH_COMP_NONE" in image_decomp(). + */ + if ( info->zimage.start != be32_to_cpu(uimage.load) ) + { + panic("Unable to support mismatching load address and entry address\n"); + return -EINVAL; + } + + /* + * While uboot considers 0x0 to be a valid load/start address, for Xen + * to mantain parity with zimage, we consider 0x0 to denote position + * independent image. That means Xen is free to load such an image at + * any valid address. + * Thus, we will print an appropriate message. + */ + if ( info->zimage.start == 0 ) + printk(XENLOG_INFO + "No load address provided. Xen will decide where to load it\n"); + info->zimage.kernel_addr = addr + sizeof(uimage); info->zimage.len = len; -- 2.17.1
