Messages in this thread | | | Subject | Re: [PATCH] tomoyo: common: Fix potential Spectre v1 vulnerability | From | Tetsuo Handa <> | Date | Thu, 1 Aug 2019 20:02:46 +0900 |
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Hello.
Thanks for a patch, but I have a question.
On 2019/08/01 3:54, Gustavo A. R. Silva wrote: > profile is controlled by user-space via /sys/kernel/security/tomoyo/profile,
It is true that "profile" value is given from user-space, and it will be true that speculative execution would access "ns->profile_ptr[profile]" before whether "profile >= TOMOYO_MAX_PROFILES" is true is concluded. But
> hence leading to a potential exploitation of the Spectre variant 1 > vulnerability.
which memory address is vulnerable to Spectre variant 1 attack? How can an attacker gain information from memory speculatively accessed by "ns->profile_ptr[profile]" ? Where is the memory access which corresponds to "arr2->data[index2]" demonstrated at https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html ?
Since I'm not familiar with Spectre/Meltdown problem, this patch sounds as if "Oh, let's suppress Smatch warning". I want to know whether this problem is real and this patch is worth keeping stable@vger.kernel.org ...
> @@ -488,13 +489,15 @@ static void tomoyo_print_number_union(struct tomoyo_io_buffer *head, > * Returns pointer to "struct tomoyo_profile" on success, NULL otherwise. > */ > static struct tomoyo_profile *tomoyo_assign_profile > -(struct tomoyo_policy_namespace *ns, const unsigned int profile) > +(struct tomoyo_policy_namespace *ns, unsigned int profile) > { > struct tomoyo_profile *ptr; > struct tomoyo_profile *entry; > > if (profile >= TOMOYO_MAX_PROFILES) > return NULL; > + profile = array_index_nospec(profile, TOMOYO_MAX_PROFILES); > + > ptr = ns->profile_ptr[profile]; > if (ptr) > return ptr; >
By the way, since /sys/kernel/security/tomoyo/profile is writable by only explicitly whitelisted domains/programs (&& by only root user by default), I think that it is OK to treat this "profile" value as trusted.
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