From: Andy Lutomirski <luto@kernel.org>
To: Jann Horn <jannh@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
kasan-dev <kasan-dev@googlegroups.com>,
LKML <linux-kernel@vger.kernel.org>,
Andrey Konovalov <andreyknvl@google.com>,
Andy Lutomirski <luto@kernel.org>,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH v2 2/3] x86/traps: Print non-canonical address on #GP
Date: Sat, 23 Nov 2019 15:07:43 -0800 [thread overview]
Message-ID: <CALCETrVQ2NqPnED_E6Y6EsCOEJJcz8GkQhgcKHk7JVAyykq06A@mail.gmail.com> (raw)
In-Reply-To: <20191115191728.87338-2-jannh@google.com>
On Fri, Nov 15, 2019 at 11:17 AM Jann Horn <jannh@google.com> wrote:
>
> A frequent cause of #GP exceptions are memory accesses to non-canonical
> addresses. Unlike #PF, #GP doesn't come with a fault address in CR2, so
> the kernel doesn't currently print the fault address for #GP.
> Luckily, we already have the necessary infrastructure for decoding X86
> instructions and computing the memory address that is being accessed;
> hook it up to the #GP handler so that we can figure out whether the #GP
> looks like it was caused by a non-canonical address, and if so, print
> that address.
>
> While it is already possible to compute the faulting address manually by
> disassembling the opcode dump and evaluating the instruction against the
> register dump, this should make it slightly easier to identify crashes
> at a glance.
>
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
>
> Notes:
> v2:
> - print different message for segment-related GP (Borislav)
> - rewrite check for non-canonical address (Sean)
> - make it clear we don't know for sure why the GP happened (Andy)
>
> arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index c90312146da0..12d42697a18e 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -56,6 +56,8 @@
> #include <asm/mpx.h>
> #include <asm/vm86.h>
> #include <asm/umip.h>
> +#include <asm/insn.h>
> +#include <asm/insn-eval.h>
>
> #ifdef CONFIG_X86_64
> #include <asm/x86_init.h>
> @@ -509,6 +511,38 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
> do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
> }
>
> +/*
> + * On 64-bit, if an uncaught #GP occurs while dereferencing a non-canonical
> + * address, print that address.
> + */
> +static void print_kernel_gp_address(struct pt_regs *regs)
> +{
> +#ifdef CONFIG_X86_64
> + u8 insn_bytes[MAX_INSN_SIZE];
> + struct insn insn;
> + unsigned long addr_ref;
> +
> + if (probe_kernel_read(insn_bytes, (void *)regs->ip, MAX_INSN_SIZE))
> + return;
> +
> + kernel_insn_init(&insn, insn_bytes, MAX_INSN_SIZE);
> + insn_get_modrm(&insn);
> + insn_get_sib(&insn);
> + addr_ref = (unsigned long)insn_get_addr_ref(&insn, regs);
> +
> + /* Bail out if insn_get_addr_ref() failed or we got a kernel address. */
> + if (addr_ref >= ~__VIRTUAL_MASK)
> + return;
> +
> + /* Bail out if the entire operand is in the canonical user half. */
> + if (addr_ref + insn.opnd_bytes - 1 <= __VIRTUAL_MASK)
> + return;
> +
> + pr_alert("probably dereferencing non-canonical address 0x%016lx\n",
> + addr_ref);
> +#endif
> +}
Could you refactor this a little bit so that we end up with a helper
that does the computation? Something like:
int probe_insn_get_memory_ref(void **addr, size_t *len, void *insn_addr);
returns 1 if there was a memory operand and fills in addr and len,
returns 0 if there was no memory operand, and returns a negative error
on error.
I think we're going to want this for #AC handling, too :)
next prev parent reply other threads:[~2019-11-23 23:08 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-15 19:17 [PATCH v2 1/3] x86/insn-eval: Add support for 64-bit kernel mode Jann Horn
2019-11-15 19:17 ` [PATCH v2 2/3] x86/traps: Print non-canonical address on #GP Jann Horn
2019-11-18 14:21 ` Borislav Petkov
2019-11-18 16:02 ` Dmitry Vyukov
2019-11-18 16:19 ` Jann Horn
2019-11-18 16:29 ` Dmitry Vyukov
2019-11-18 16:40 ` error attribution for stalls [was: [PATCH v2 2/3] x86/traps: Print non-canonical address on #GP] Jann Horn
2019-11-18 16:44 ` [PATCH v2 2/3] x86/traps: Print non-canonical address on #GP Borislav Petkov
2019-11-18 17:38 ` Borislav Petkov
2019-11-20 11:41 ` Ingo Molnar
2019-11-20 11:40 ` Ingo Molnar
2019-11-20 11:52 ` Borislav Petkov
2019-11-20 4:25 ` Andi Kleen
2019-11-20 10:31 ` Jann Horn
2019-11-20 13:56 ` Andi Kleen
2019-11-20 14:24 ` Jann Horn
2019-11-23 23:07 ` Andy Lutomirski [this message]
2019-11-27 20:27 ` Jann Horn
2019-11-28 5:23 ` Andy Lutomirski
2019-11-15 19:17 ` [PATCH v2 3/3] x86/kasan: Print original " Jann Horn
2019-11-18 8:36 ` Dmitry Vyukov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CALCETrVQ2NqPnED_E6Y6EsCOEJJcz8GkQhgcKHk7JVAyykq06A@mail.gmail.com \
--to=luto@kernel.org \
--cc=andreyknvl@google.com \
--cc=aryabinin@virtuozzo.com \
--cc=bp@alien8.de \
--cc=dvyukov@google.com \
--cc=glider@google.com \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=kasan-dev@googlegroups.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=sean.j.christopherson@intel.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).