Re: [PATCH] arm64: trap illegal translations in __virt_to_phys()
From: Miles Chen
Date: Mon Jan 07 2019 - 22:25:02 EST
On Mon, 2019-01-07 at 15:00 +0000, Mark Rutland wrote:
> On Mon, Jan 07, 2019 at 07:21:20PM +0800, Miles Chen wrote:
> > Current __virt_to_phys() only print warning messages for non-linear
> > addresses. It's hard to catch all warnings by those messages.
> Why? Are you seeing a large number of warnings somewhere?
Official kernel works fine. I saw some cases in our internal branch and
we're fixing them.
> > So add a VIRTUAL_BUG_ON() to trap all non-linear and non-symbol
> > addresses (e.g., stack addresses)
> > Tested by pass stack addresses and symbol addresses to __pa(). Result:
> > stack addresses: kernel BUG()
> * Stacks are vmap'd, and __is_lm_address(stack_addr) is false. We'll
> produce a WARNING() today (and return a junk physical address).
> * Stacks are linear mapped, and cannot be distinguished from other
> linear mapped addresses. The physical address will be valid.
> ... so I don't understand why you need to change this.
For the first case: for vmap'd stack, __pa() returns a junk
physical address and it might be easier to debug this incorrect address
translation by a BUG() call instead of monitoring the warning log.
Like __phys_addr_symbol() does. __phys_addr_symbol() uses
VIRTUAL_BUG_ON() for non symbol addresses.
> > symbol addresses: kernel warning message
> That should already be the case today, since the kernel image is mapped
> separately from the linear map, so __is_lm_address(symbol_addr) should
> be false.
> > Maybe we should trap all non-linear address translations in the future.
> > Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
> > ---
> > arch/arm64/mm/physaddr.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> > diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c
> > index 67a9ba9eaa96..f6b935dad19c 100644
> > --- a/arch/arm64/mm/physaddr.c
> > +++ b/arch/arm64/mm/physaddr.c
> > @@ -14,6 +14,11 @@ phys_addr_t __virt_to_phys(unsigned long x)
> > (void *)x,
> > (void *)x);
> > + /* trap all non-linear and non-symbol addresses */
> > + VIRTUAL_BUG_ON(!__is_lm_address(x) &&
> > + (x < (unsigned long)KERNEL_START ||
> > + x > (unsigned long)KERNEL_END));
> The KERNEL_START and KERNEL_END definitions refer to the kernel image,
> not the linear map, so it doesn't make any sense to permit those here.
> It is *not* valid to call __virt_to_phys() with a symbol address. We
> only support those in __virt_to_phys_nodebug() so that broken code has a
> chance of stumbling on.
> If you want the kernel to die immediately when it hits a warning here,
> please set panic_on_warn.