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powerpc/mm/hash: Handle user access of kernel address gracefully

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In commit 2865d08dd9 ("powerpc/mm: Move the DSISR_PROTFAULT sanity
check") we moved the protection fault access check before the vma
lookup. That means we hit that WARN_ON when user space accesses a
kernel address. Before that commit this was handled by find_vma() not
finding vma for the kernel address and considering that access as bad
area access.

Avoid the confusing WARN_ON and convert that to a ratelimited printk.

With the patch we now get:

for load:
  a.out[5997]: User access of kernel address (c00000000000dea0) - exploit attempt? (uid: 1000)
  a.out[5997]: segfault (11) at c00000000000dea0 nip 1317c0798 lr 7fff80d6441c code 1 in a.out[1317c0000+10000]
  a.out[5997]: code: 60000000 60420000 3c4c0002 38427790 4bffff20 3c4c0002 38427784 fbe1fff8
  a.out[5997]: code: f821ffc1 7c3f0b78 60000000 e9228030 <89290000> 993f002f 60000000 383f0040

for exec:
  a.out[6067]: User access of kernel address (c00000000000dea0) - exploit attempt? (uid: 1000)
  a.out[6067]: segfault (11) at c00000000000dea0 nip c00000000000dea0 lr 129d507b0 code 1
  a.out[6067]: Bad NIP, not dumping instructions.

Fixes: 2865d08dd9 ("powerpc/mm: Move the DSISR_PROTFAULT sanity check")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Tested-by: Breno Leitao <leitao@debian.org>
[mpe: Don't split printk() string across lines]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Aneesh Kumar K.V 2018-11-26 20:05:04 +05:30 committed by Michael Ellerman
parent 385e89d5b2
commit 374f3f5979
1 changed files with 19 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

24
arch/powerpc/mm/fault.c
View file

@ -342,8 +342,19 @@ static inline void cmo_account_page_fault(void) { }
#endif /* CONFIG_PPC_SMLPAR */
#ifdef CONFIG_PPC_BOOK3S
static void sanity_check_fault(bool is_write, unsigned long error_code)
static void sanity_check_fault(bool is_write, bool is_user,
unsigned long error_code, unsigned long address)
{
/*
* Userspace trying to access kernel address, we get PROTFAULT for that.
*/
if (is_user && address >= TASK_SIZE) {
pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
current->comm, current->pid, address,
from_kuid(&init_user_ns, current_uid()));
return;
}
/*
* For hash translation mode, we should never get a
* PROTFAULT. Any update to pte to reduce access will result in us
@ -373,11 +384,14 @@ static void sanity_check_fault(bool is_write, unsigned long error_code)
* For radix, we can get prot fault for autonuma case, because radix
* page table will have them marked noaccess for user.
*/
if (!radix_enabled() && !is_write)
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
if (radix_enabled() || is_write)
return;
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}
#else
static void sanity_check_fault(bool is_write, unsigned long error_code) { }
static void sanity_check_fault(bool is_write, bool is_user,
unsigned long error_code, unsigned long address) { }
#endif /* CONFIG_PPC_BOOK3S */
/*
@ -435,7 +449,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
}
/* Additional sanity check(s) */
sanity_check_fault(is_write, error_code);
sanity_check_fault(is_write, is_user, error_code, address);
/*
* The kernel should never take an execute fault nor should it