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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LOWpAtDoTm28o2tE/1stUtYVbc0rRPQchkrnlB7RW/S9U6SE5nUU0Fwcrw4OOJ2K+ UHaD7IDWwYQSmFPfnOcf1eWhmM/bJE29QgK2J4WEgNqxJW8XEzaQNhlFk6wJOsnBd8 O1ttBL/Yxwa/JKbvG6S2DgbbCRHIYjFfwWgXN3Ko= Message-ID: Date: Thu, 23 Jul 2026 11:27:18 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/usercopy: harden bounds checking for vmalloc allocations To: Kees Cook Cc: akpm@linux-foundation.org, gustavoars@kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, david@kernel.org, urezki@gmail.com References: <20260722142936.3287702-1-dev.jain@arm.com> <202607222102.E6A5679@keescook> Content-Language: en-US From: Dev Jain In-Reply-To: <202607222102.E6A5679@keescook> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 2EE1620005 X-Stat-Signature: 9perzhpn8ztsp7k4w1jy4iakswq1rgqz X-Rspam-User: X-HE-Tag: 1784786245-341907 X-HE-Meta: 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 yD/a67yz b3Hqrx5u6ltoHY2s+z1VBkiutq47xdpG9ZXsxs/2zRC28BhBBsNRDvGX+O9qUefWO6GICYshne+ecUyCxllw2A255ttN8xZYf86c4GnVU4kPD4g0lygf8wHK8mmrjl+QaVPWx2Dn2xrxp1lw1VW73XbVV/uoPVtDczNILHbcnFn6fJQqwrZ+/a7HbzT6Ko37oB96eJgBcZeaes0J3jOMkGLd3crsonuJ/E0/iKKSS6iUX3Ic9cNfpBD7Pe9udomTJjAFs0cwpMrCtT0tPYtWCAI39emkwMvIUk7h3 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 23/07/26 9:33 am, Kees Cook wrote: > On Wed, Jul 22, 2026 at 02:29:35PM +0000, Dev Jain wrote: >> The vmalloc allocator stores the actual allocation size inside the >> vm_struct structure. We can use this bound in usercopy instead of the >> page-aligned va_end to catch usercopy beyond the actual allocation size. >> >> For vmap, the requested_size field is always page-aligned since it maps a >> certain number of pages. Same for vm_map_ram (alongwith, not even having >> a vm_struct). So the check is only relevant for vmalloc mappings. >> >> Because there are early vm areas registered even before vmalloc_init, >> requested_size may be zero. So also check whether the requested_size >> is set. >> >> Signed-off-by: Dev Jain > > Looks good to me! Can you update the LKDTM tests to check for this more > tightened range check with a new vmalloc-based test? Thanks. I have written the test, I'll send a v2 with it once the mm people take a look at this. > > If other mm folks can double-check this, I'll happily take this via the > hardening tree. > > Thanks! > > -Kees > >> --- >> Applies on mm-new (3d18f3499c48). >> >> mm/usercopy.c | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/mm/usercopy.c b/mm/usercopy.c >> index 5de7a518b1b1c..772681aff8477 100644 >> --- a/mm/usercopy.c >> +++ b/mm/usercopy.c >> @@ -176,10 +176,28 @@ static inline void check_heap_object(const void *ptr, unsigned long n, >> >> if (is_vmalloc_addr(ptr) && !pagefault_disabled()) { >> struct vmap_area *area = find_vmap_area(addr); >> + struct vm_struct *vm; >> >> if (!area) >> usercopy_abort("vmalloc", "no area", to_user, 0, n); >> >> + vm = area->vm; >> + /* >> + * Mappings with a vm_struct track the originally requested >> + * size. Check against that rather than the page-rounded >> + * vmap_area->va_end so copies cannot reach vmalloc tail >> + * padding. vmap mappings are always page aligned. >> + */ >> + if (vm && (vm->flags & VM_ALLOC) && vm->requested_size) { >> + unsigned long size = vm->requested_size; >> + >> + offset = addr - area->va_start; >> + if (offset > size || n > size - offset) >> + usercopy_abort("vmalloc", NULL, to_user, >> + offset, n); >> + return; >> + } >> + >> if (n > area->va_end - addr) { >> offset = addr - area->va_start; >> usercopy_abort("vmalloc", NULL, to_user, offset, n); >> -- >> 2.43.0 >> >