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:
---
>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>
---
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
--
2.27.0
