From: Andrew Cooper <email@example.com> To: Jan Beulich <firstname.lastname@example.org> Cc: George Dunlap <George.Dunlap@eu.citrix.com>, Ian Jackson <email@example.com>, Stefano Stabellini <firstname.lastname@example.org>, Wei Liu <email@example.com>, Julien Grall <firstname.lastname@example.org>, Dario Faggioli <email@example.com>, Xen-devel <firstname.lastname@example.org> Subject: Re: [PATCH 1/6] xen/trace: Don't over-read trace objects Date: Mon, 20 Sep 2021 11:24:45 +0100 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> On 20/09/2021 09:00, Jan Beulich wrote: > On 17.09.2021 15:26, Andrew Cooper wrote: >> On 17/09/2021 13:58, Jan Beulich wrote: >>> On 17.09.2021 10:45, Andrew Cooper wrote: >>>> --- a/xen/common/trace.c >>>> +++ b/xen/common/trace.c >>>> @@ -686,22 +686,21 @@ void __trace_var(u32 event, bool_t cycles, unsigned int extra, >>>> unsigned long flags; >>>> u32 bytes_to_tail, bytes_to_wrap; >>>> unsigned int rec_size, total_size; >>>> - unsigned int extra_word; >>>> bool_t started_below_highwater; >>>> >>>> if( !tb_init_done ) >>>> return; >>>> >>>> - /* Convert byte count into word count, rounding up */ >>>> - extra_word = (extra / sizeof(u32)); >>>> - if ( (extra % sizeof(u32)) != 0 ) >>>> - extra_word++; >>>> - >>>> - ASSERT(extra_word <= TRACE_EXTRA_MAX); >>>> - extra_word = min_t(int, extra_word, TRACE_EXTRA_MAX); >>>> - >>>> - /* Round size up to nearest word */ >>>> - extra = extra_word * sizeof(u32); >>>> + /* >>>> + * Trace records require extra data which is an exact multiple of >>>> + * uint32_t. Reject out-of-spec records. Any failure here is an error in >>>> + * the caller. >>>> + */ >>> Hmm, is "require" accurate? >> In terms of "what will go wrong if this condition is violated", yes. >> >>> They may very well come without extra data >>> afaics. >> 0 is fine, and used by plenty of records, and also permitted by the >> filtering logic. > I was about to say that the two parts of your reply contradict one > another, when I finally realized that it looks like the first sentence > in the comment can be read two ways: "Trace records require extra data" > then going on to describe properties, or "Trace records require extra > data to be an exact multiple of uint32_t." Obviously this is to me as a > non-native speaker. But maybe you could still reword this to be > unambiguous? (I'm not going to exclude that the lack of a comma, which > I did silently add while reading, makes a difference here: Does "Trace > records require extra data, which is an exact multiple of uint32_t" end > up altering the meaning?) Yes. The requirement is for "extra data which is an exact multiple of uint32_t", not "extra data". The comma massively changes the meaning. I'll see about tweaking the wording. ~Andrew
next prev parent reply other threads:[~2021-09-20 10:25 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-17 8:45 [PATCH 0/6] xen/trace: Fix leakage of uninitialised stack into the tracebuffer Andrew Cooper 2021-09-17 8:45 ` [PATCH 1/6] xen/trace: Don't over-read trace objects Andrew Cooper 2021-09-17 12:58 ` Jan Beulich 2021-09-17 13:26 ` Andrew Cooper 2021-09-20 8:00 ` Jan Beulich 2021-09-20 10:24 ` Andrew Cooper [this message] 2021-09-17 8:45 ` [PATCH 2/6] xen/memory: Remove tail padding from TRC_MEM_* records Andrew Cooper 2021-09-17 13:04 ` Jan Beulich 2021-09-17 8:45 ` [PATCH 3/6] xen/credit2: Remove tail padding from TRC_CSCHED2_* records Andrew Cooper 2021-09-17 13:10 ` Jan Beulich 2021-09-17 13:28 ` Andrew Cooper 2021-09-17 8:45 ` [PATCH 4/6] x86/trace: Reduce stack usage from HVMTRACE_ND() Andrew Cooper 2021-09-20 9:05 ` Jan Beulich 2021-09-20 11:02 ` Andrew Cooper 2021-09-20 13:00 ` Jan Beulich 2021-09-17 8:45 ` [PATCH 5/6] xen/credit2: Clean up trace handling Andrew Cooper 2021-09-20 9:11 ` Jan Beulich 2021-09-17 8:45 ` [PATCH 6/6] xen/trace: Minor code cleanup Andrew Cooper 2021-09-20 9:15 ` Jan Beulich
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