From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Fri, 18 Aug 2017 16:35:31 +0100 Subject: [PATCH] arm64: kaslr: Adjust the offset to avoid Image across alignment boundary In-Reply-To: References: <20170818150435.35224-1-catalin.marinas@arm.com> <20170818151920.jpugpcgwiavgwgaf@armageddon.cambridge.arm.com> <20170818152257.dbllbeuxwm5nugno@armageddon.cambridge.arm.com> Message-ID: <20170818153531.GA22970@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Aug 18, 2017 at 04:24:46PM +0100, Ard Biesheuvel wrote: > On 18 August 2017 at 16:22, Catalin Marinas wrote: > > On Fri, Aug 18, 2017 at 04:20:16PM +0100, Ard Biesheuvel wrote: > >> On 18 August 2017 at 16:19, Catalin Marinas wrote: > >> > On Fri, Aug 18, 2017 at 04:04:34PM +0100, Catalin Marinas wrote: > >> >> With 16KB pages and a kernel Image larger than 16MB, the current > >> >> kaslr_early_init() logic for avoiding mappings across swapper table > >> >> boundaries fails since increasing the offset by kimg_sz just moves the > >> >> problem to the next boundary. > >> >> > >> >> This patch decreases the offset by the boundary overflow amount, with > >> >> slight risk of reduced entropy as the kernel is more likely to be found > >> >> at kimg_sz below a swapper table boundary. > >> >> > >> >> Trying-to-fix: afd0e5a87670 ("arm64: kaslr: Fix up the kernel image alignment") > >> >> Cc: Ard Biesheuvel > >> >> Cc: Mark Rutland > >> >> Cc: Will Deacon > >> >> Cc: Neeraj Upadhyay > >> >> Signed-off-by: Catalin Marinas > >> >> --- > >> >> > >> >> While preparing this email, I noticed that the kernel eventually failed > >> >> to boot, though after a lot more reboot iterations. Mark Rutland also > >> >> managed to make the KASLR kernel fail to boot with 64K pages which > >> >> wouldn't be explained by this patch. > >> >> > >> >> So, any suggestions are welcome. My testing method, qemu starting a > >> >> guest in a loop with virtio-rng-pci. > >> > > >> > Apparently, the booting gets much more stable if I disable the physical > >> > relocation in arm64-stub.c (but keep the virtual one with the fix in > >> > this patch). So I guess we are chasing two different issues. > >> > >> So this is using QEMU with 16k pages support? > > > > Qemu running on a ThunderX, so native KVM support. > > > > Ah ok. I did not realize QEMU supports 16 KB pages in that case. Nice! > > However, that makes it rather difficult to reproduce on my side. FWIW, I was testing with 64K pages, under QEMU+KVM on a SoftIrorn OverDrive 1000 (i.e. a 4-core A57 system). I'd hacked early_kaslr_init() so that I could override the seed on the command line. I accidentally blatted that hack, but hopefully the below is equivalent. I had a script that iterated the seed in 2M increments, launch a VM for each seed. The fileststem was configured to power down immediately once it reached userspace. I found that it hung with seed value: 0x0000000016c00000, which would generate an offset of 0x17e00000. I tried nearby seeds, which worked: seed offset 0x0000000016a00000 0x16a00000 worked 0x0000000016c00000 0x17e00000 failed 0x0000000016e00000 0x18000000 worked ... but I assume that failing values are dependent on the kernel Image layout. Thanks, Mark. ---->8---- t a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c index a9710ef..df50442 100644 --- a/arch/arm64/kernel/kaslr.c +++ b/arch/arm64/kernel/kaslr.c @@ -102,8 +102,8 @@ u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) * Retrieve (and wipe) the seed from the FDT */ seed = get_kaslr_seed(fdt); - if (!seed) - return 0; + //if (!seed) + // return 0; /* * Check if 'nokaslr' appears on the command line, and @@ -114,6 +114,12 @@ u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) return 0; + str = strstr(cmdline, "kaslr_seed=") + if (str) { + str += strlen("kaslr_seed="); + seed = simple_strtoull(str, NULL, 16); + } + /* * OK, so we are proceeding with KASLR enabled. Calculate a suitable * kernel image offset from the seed. Let's place the kernel in the