On 7/20/20 9:58 PM, Christoph Hellwig wrote: > On Mon, Jul 20, 2020 at 03:10:46PM -0700, Guenter Roeck wrote: >> I had another look into the code. Right after this patch, I see >> >> #define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS) >> >> Yet, this patch is: >> >> - if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS), >> + if (CHECK_DATA_CORRUPTION(uaccess_kernel(), >> >> So there is a negation in the condition. Indeed, the following change >> on top of next-20200720 fixes the problem for mps2-an385. >> >> - if (CHECK_DATA_CORRUPTION(uaccess_kernel(), >> + if (CHECK_DATA_CORRUPTION(!uaccess_kernel(), >> >> How does this work anywhere ? > > No, that is the wrong check - we want to make sure the address > space override doesn't leak to userspace. The problem is that > armnommu (and m68knommu, but that doesn't call the offending > function) pretends to not have a kernel address space, which doesn't > really work. Here is the fix I sent out yesterday, which I should > have Cc'ed you on, sorry: > The patch below makes sense, and it does work, but I still suspect that something with your original patch is wrong, or at least suspicious. Reason: My change above (Adding the "!") works for _all_ of my arm boot tests. Or, in other words, it doesn't make a difference if true or false is passed as first parameter of CHECK_DATA_CORRUPTION(), except for nommu systems. Also, unless I am really missing something, your original patch _does_ reverse the logic. I didn't track this down further. Thanks, Guenter > --- >>From 2bb889b2d99a2d978e90640ade8fe02359287092 Mon Sep 17 00:00:00 2001 > From: Christoph Hellwig <hch@xxxxxx> > Date: Mon, 20 Jul 2020 17:46:50 +0200 > Subject: arm: don't call addr_limit_user_check for nommu > > On arm nommu kernel use the same constant for USER_DS and KERNEL_DS, > and seqment_eq always returns false. With the current check in > addr_limit_user_check that works by accident, but when replacing > seqment_eq with uaccess_kerne it will fail. Just remove the not > needed check entirely. > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx> Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> > --- > arch/arm/kernel/signal.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c > index ab2568996ddb0c..c9dc912b83f012 100644 > --- a/arch/arm/kernel/signal.c > +++ b/arch/arm/kernel/signal.c > @@ -713,7 +713,9 @@ struct page *get_signal_page(void) > /* Defer to generic check */ > asmlinkage void addr_limit_check_failed(void) > { > +#ifdef CONFIG_MMU > addr_limit_user_check(); > +#endif > } > > #ifdef CONFIG_DEBUG_RSEQ >