From: Christophe Leroy christophe.leroy@csgroup.eu
stable inclusion from stable-v5.4.133 commit a82471a14aad90f79d1608d2bcbb019f0ffb53f0 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9R4CI CVE: CVE-2021-47350
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit cd5d5e602f502895e47e18cd46804d6d7014e65c upstream.
The powerpc kernel is not prepared to handle exec faults from kernel. Especially, the function is_exec_fault() will return 'false' when an exec fault is taken by kernel, because the check is based on reading current->thread.regs->trap which contains the trap from user.
For instance, when provoking a LKDTM EXEC_USERSPACE test, current->thread.regs->trap is set to SYSCALL trap (0xc00), and the fault taken by the kernel is not seen as an exec fault by set_access_flags_filter().
Commit d7df2443cd5f ("powerpc/mm: Fix spurious segfaults on radix with autonuma") made it clear and handled it properly. But later on commit d3ca587404b3 ("powerpc/mm: Fix reporting of kernel execute faults") removed that handling, introducing test based on error_code. And here is the problem, because on the 603 all upper bits of SRR1 get cleared when the TLB instruction miss handler bails out to ISI.
Until commit cbd7e6ca0210 ("powerpc/fault: Avoid heavy search_exception_tables() verification"), an exec fault from kernel at a userspace address was indirectly caught by the lack of entry for that address in the exception tables. But after that commit the kernel mainly relies on KUAP or on core mm handling to catch wrong user accesses. Here the access is not wrong, so mm handles it. It is a minor fault because PAGE_EXEC is not set, set_access_flags_filter() should set PAGE_EXEC and voila. But as is_exec_fault() returns false as explained in the beginning, set_access_flags_filter() bails out without setting PAGE_EXEC flag, which leads to a forever minor exec fault.
As the kernel is not prepared to handle such exec faults, the thing to do is to fire in bad_kernel_fault() for any exec fault taken by the kernel, as it was prior to commit d3ca587404b3.
Fixes: d3ca587404b3 ("powerpc/mm: Fix reporting of kernel execute faults") Cc: stable@vger.kernel.org # v4.14+ Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu Acked-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/024bb05105050f704743a0083fe3548702be5706.162513820... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Conflicts: arch/powerpc/mm/fault.c [ Context conflicts due to lack of commit de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection"). ] Signed-off-by: Liu Shixin liushixin2@huawei.com --- arch/powerpc/mm/fault.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 5b04d029f824..41f1de87edb6 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -221,9 +221,7 @@ static int mm_fault_error(struct pt_regs *regs, unsigned long addr, static bool bad_kernel_fault(bool is_exec, unsigned long error_code, unsigned long address) { - /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */ - if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT | - DSISR_PROTFAULT))) { + if (is_exec) { printk_ratelimited(KERN_CRIT "kernel tried to execute" " exec-protected page (%lx) -" "exploit attempt? (uid: %d)\n",