On Thu, Feb 23, 2023 at 09:41:01PM +0100, Ard Biesheuvel wrote: > Our virtual KASLR displacement is a randomly chosen multiple of > 2 MiB plus an offset that is equal to the physical placement modulo 2 > MiB. This arrangement ensures that we can always use 2 MiB block > mappings (or contiguous PTE mappings for 16k or 64k pages) to map the > kernel. > > This means that a KASLR offset of less than 2 MiB is simply the product > of this physical displacement, and no randomization has actually taken > place. Currently, we use 'kaslr_offset() > 0' to decide whether or not > randomization has occurred, and so we misidentify this case. > Fix this, by correctly identifying the case where the virtual > displacement is a result of the physical displacement only. > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Mark. > --- > I have sent out the same patch with a much shorter commit log as part of > my LPA2 series before, but I only realized today that this is likely to > fix most occurrences of the issue where a single 10g vmalloc() call > break subsequent module loading, so I am reposting it in isolation. > > arch/arm64/include/asm/memory.h | 11 +++++++++++ > arch/arm64/kernel/cpufeature.c | 2 +- > arch/arm64/kernel/kaslr.c | 2 +- > 3 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 9dd08cd339c3f028..78e5163836a0ab95 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -180,6 +180,7 @@ > #include <linux/compiler.h> > #include <linux/mmdebug.h> > #include <linux/types.h> > +#include <asm/boot.h> > #include <asm/bug.h> > > #if VA_BITS > 48 > @@ -203,6 +204,16 @@ static inline unsigned long kaslr_offset(void) > return kimage_vaddr - KIMAGE_VADDR; > } > > +static inline bool kaslr_enabled(void) > +{ > + /* > + * The KASLR offset modulo MIN_KIMG_ALIGN is taken from the physical > + * placement of the image rather than from the seed, so a displacement > + * of less than MIN_KIMG_ALIGN means that no seed was provided. > + */ > + return kaslr_offset() >= MIN_KIMG_ALIGN; > +} > + > /* > * Allow all memory at the discovery stage. We will clip it later. > */ > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 45a42cf2191c36c3..5643a9ca502af207 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1633,7 +1633,7 @@ bool kaslr_requires_kpti(void) > return false; > } > > - return kaslr_offset() > 0; > + return kaslr_enabled(); > } > > static bool __meltdown_safe = true; > diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c > index 325455d16dbcb31a..e7477f21a4c9d062 100644 > --- a/arch/arm64/kernel/kaslr.c > +++ b/arch/arm64/kernel/kaslr.c > @@ -41,7 +41,7 @@ static int __init kaslr_init(void) > return 0; > } > > - if (!kaslr_offset()) { > + if (!kaslr_enabled()) { > pr_warn("KASLR disabled due to lack of seed\n"); > return 0; > } > -- > 2.39.1 >