From: Laura Abbott <labbott@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: kernel-hardening@lists.openwall.com,
LKML <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>, X86 ML <x86@kernel.org>
Subject: Re: [RFC PATCH 2/2] x86: Allow paranoid __{get,put}_user
Date: Mon, 6 Nov 2017 12:38:08 -0800 [thread overview]
Message-ID: <228e1cbb-ec61-b54a-4093-2d377e90ca6b@redhat.com> (raw)
In-Reply-To: <CAGXu5jJconGeCQbRX9XOpPo__dgDY5zdRtb5G6ce7Wih7SHyiQ@mail.gmail.com>
On 11/03/2017 05:14 PM, Kees Cook wrote:
> On Fri, Nov 3, 2017 at 4:04 PM, Laura Abbott <labbott@redhat.com> wrote:
>> __{get,put}_user calls are designed to be fast and have no checks,
>> relying on the caller to have made the appropriate calls previously.
>> It's very easy to forget a check though, leaving the kernel vulnerable
>> to exploits. Add an option to do the checks and kill the kernel if it
>> catches something bad.
>>
>> Signed-off-by: Laura Abbott <labbott@redhat.com>
>> ---
>> This is the actual implemtation for __{get,put}_user on x86 based on
>> Mark Rutland's work for arm66
>> lkml.kernel.org/r/<20171026090942.7041-1-mark.rutland@arm.com>
>>
>> x86 turns out to be easier since the safe and unsafe paths are mostly
>> disjoint so we don't have to worry about gcc optimizing out access_ok.
>> I tweaked the Kconfig to someting a bit more generic.
>>
>> The size increase was ~8K in text with a config I tested.
>
> Specifically, this feature would have caught the waitid() bug in 4.13
> immediately.
>
>> ---
>> arch/x86/Kconfig | 3 +++
>> arch/x86/include/asm/uaccess.h | 11 ++++++++++-
>> security/Kconfig | 11 +++++++++++
>> 3 files changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 2fdb23313dd5..10c6e150a91e 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -261,6 +261,9 @@ config RWSEM_XCHGADD_ALGORITHM
>> config GENERIC_CALIBRATE_DELAY
>> def_bool y
>>
>> +config ARCH_HAS_PARANOID_UACCESS
>> + def_bool y
>> +
>> config ARCH_HAS_CPU_RELAX
>> def_bool y
>>
>> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
>> index d23fb5844404..767febe1c720 100644
>> --- a/arch/x86/include/asm/uaccess.h
>> +++ b/arch/x86/include/asm/uaccess.h
>> @@ -132,6 +132,13 @@ extern int __get_user_bad(void);
>> #define __inttype(x) \
>> __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
>>
>> +
>> +#define verify_uaccess(dir, ptr) \
>> +({ \
>> + if (IS_ENABLED(CONFIG_PARANOID_UACCESS)) \
>> + BUG_ON(!access_ok(dir, (ptr), sizeof(*(ptr)))); \
>> +})
>> +
>> /**
>> * get_user: - Get a simple variable from user space.
>> * @x: Variable to store result.
>> @@ -278,6 +285,7 @@ do { \
>> typeof(ptr) __pu_ptr = (ptr); \
>> retval = 0; \
>> __chk_user_ptr(__pu_ptr); \
>> + verify_uaccess(VERIFY_WRITE, __pu_ptr); \
>> switch (size) { \
>> case 1: \
>> __put_user_asm(x, __pu_ptr, retval, "b", "b", "iq", \
>> @@ -293,7 +301,7 @@ do { \
>> break; \
>> case 8: \
>> __put_user_asm_u64((__typeof__(*ptr))(x), __pu_ptr, \
>> - retval, \ errret); \
>> + retval, errret); \
>> break; \
>> default: \
>> __put_user_bad(); \
>
> Which tree is this against? I don't see the weird line break in my tree?
>
Uggggh I meant to fold this into the previous patch.
>> @@ -359,6 +367,7 @@ do { \
>> typeof(ptr) __gu_ptr = (ptr); \
>> retval = 0; \
>> __chk_user_ptr(__gu_ptr); \
>> + verify_uaccess(VERIFY_READ, __gu_ptr); \
>> switch (size) { \
>> case 1: \
>> __get_user_asm(x, __gu_ptr, retval, "b", "b", "=q", \
>
> Does __put/get_user_size_ex() need additions too? (And does
> put/get_user_ex() lack access_ok() checks as-is? Looks like the users
> are have access_ok() checks, but that naming really shouldn't be
> aliased to "put/get_user_ex" -- otherwise it gives the impression it's
> doing access_ok() checks...)
>
Possibly? A better approach might be to add the check to uaccess_try
which is where all the users already are. The users of these APIs are
pretty limited and I doubt they'd get used randomly.
Thanks,
Laura
prev parent reply other threads:[~2017-11-06 20:38 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 9:09 [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks Mark Rutland
2017-10-26 9:09 ` [RFC PATCH 1/2] arm64: write __range_ok() in C Mark Rutland
2017-11-16 15:28 ` Will Deacon
2017-11-20 12:22 ` Mark Rutland
2017-10-26 9:09 ` [RFC PATCH 2/2] arm64: allow paranoid __{get,put}user Mark Rutland
2017-10-27 15:41 ` [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks Will Deacon
2017-10-27 20:44 ` Mark Rutland
2017-10-28 8:47 ` Russell King - ARM Linux
2017-10-31 23:56 ` Laura Abbott
2017-11-01 12:05 ` Mark Rutland
2017-11-01 21:13 ` Laura Abbott
2017-11-01 22:28 ` Kees Cook
2017-11-01 23:05 ` Laura Abbott
2017-11-01 23:29 ` Kees Cook
2017-11-02 1:25 ` Laura Abbott
2017-11-03 23:04 ` [RFC PATCH 1/2] x86: Avoid multiple evaluations in __{get,put}_user_size Laura Abbott
2017-11-03 23:04 ` [RFC PATCH 2/2] x86: Allow paranoid __{get,put}_user Laura Abbott
2017-11-04 0:14 ` Kees Cook
2017-11-04 0:24 ` Al Viro
2017-11-04 0:44 ` Al Viro
2017-11-04 1:39 ` Kees Cook
2017-11-04 1:41 ` Kees Cook
2017-11-04 1:58 ` Mark Rutland
2017-11-06 20:38 ` Laura Abbott [this message]
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