From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Date: Fri, 18 Aug 2017 10:30:30 +0000 Subject: [PATCH] x86/ldt: Off by one in get_segment_base() Message-Id: <20170818102516.gqwm4xdvvuvjw5ho@mwanda> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Zijlstra Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org ldt->entries[] is allocated in alloc_ldt_struct(). It has ldt->nr_entries elements and ldt->nr_entries is capped at LDT_ENTRIES. So if "idx" is = ldt->nr_entries then we're reading beyond the end of the buffer. It seems duplicative to have two limit checks when one would work just as well so I removed the check against LDT_ENTRIES. The gdt_page.gdt[] array has GDT_ENTRIES entries. Fixes: d07bdfd322d3 ("perf/x86: Fix USER/KERNEL tagging of samples properly") Signed-off-by: Dan Carpenter --- This is a static checker fix. I'm pretty certain it's correct. But I don't understand the code terribly well, so please let me know and I'll be happy to send a v2 if needed. diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index af12e294caed..939050169d12 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2335,12 +2335,9 @@ static unsigned long get_segment_base(unsigned int segment) #ifdef CONFIG_MODIFY_LDT_SYSCALL struct ldt_struct *ldt; - if (idx > LDT_ENTRIES) - return 0; - /* IRQs are off, so this synchronizes with smp_store_release */ ldt = lockless_dereference(current->active_mm->context.ldt); - if (!ldt || idx > ldt->nr_entries) + if (!ldt || idx >= ldt->nr_entries) return 0; desc = &ldt->entries[idx]; @@ -2348,7 +2345,7 @@ static unsigned long get_segment_base(unsigned int segment) return 0; #endif } else { - if (idx > GDT_ENTRIES) + if (idx >= GDT_ENTRIES) return 0; desc = raw_cpu_ptr(gdt_page.gdt) + idx;