Date: Fri, 8 Jan 2016 11:25:14 +0100 From: Ard Biesheuvel <ard.biesheuvel@...aro.org> To: James Morse <james.morse@....com> Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, kernel-hardening@...ts.openwall.com, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, Leif Lindholm <leif.lindholm@...aro.org>, Kees Cook <keescook@...omium.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Stuart Yoder <stuart.yoder@...escale.com>, Sharma Bhupesh <bhupesh.sharma@...escale.com>, Arnd Bergmann <arnd@...db.de>, Marc Zyngier <marc.zyngier@....com>, Christoffer Dall <christoffer.dall@...aro.org> Subject: Re: [PATCH v2 12/13] arm64: add support for relocatable kernel On 8 January 2016 at 11:17, James Morse <james.morse@....com> wrote: > Hi Ard! > > On 30/12/15 15:26, Ard Biesheuvel wrote: >> This adds support for runtime relocation of the kernel Image, by >> building it as a PIE (ET_DYN) executable and applying the dynamic >> relocations in the early boot code. >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org> >> --- > >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> index 01a33e42ed70..ab582ee58b58 100644 >> --- a/arch/arm64/kernel/head.S >> +++ b/arch/arm64/kernel/head.S >> @@ -243,6 +253,16 @@ ENDPROC(stext) >> preserve_boot_args: >> mov x21, x0 // x21=FDT >> >> +#ifdef CONFIG_ARM64_RELOCATABLE_KERNEL >> + /* >> + * Mask off the bits of the random value supplied in x1 so it can serve >> + * as a KASLR displacement value which will move the kernel image to a >> + * random offset in the lower half of the VMALLOC area. >> + */ >> + mov x23, #(1 << (VA_BITS - 2)) - 1 >> + and x23, x23, x1, lsl #SWAPPER_BLOCK_SHIFT >> +#endif > > I've managed to make this fail to boot by providing a seed that caused > the kernel to overlap a 1G boundary on a 4K system. > Ah, yes. Thanks for spotting that. > (It looks like your v3 may have the same issue - but I haven't tested it.) > > Yes, it does. It probably makes sense to sacrifice some entropy bits and simply round up the kaslr offset to a log2 upper bound of the kernel Image size, rather than hacking up some logic in assembly to test whether we are crossing a PMD/PUD boundary >> + >> adr_l x0, boot_args // record the contents of >> stp x21, x1, [x0] // x0 .. x3 at kernel entry >> stp x2, x3, [x0, #16] > > > Thanks! > > James >
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.