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[50.253.99.174]) by smtp.gmail.com with ESMTPSA id a8sm6945151ilh.5.2021.10.18.12.01.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Oct 2021 12:01:41 -0700 (PDT) From: Warner Losh To: qemu-devel@nongnu.org Subject: [PULL v2 07/23] bsd-user/mmap.c: Don't mmap fd == -1 independently from MAP_ANON flag Date: Mon, 18 Oct 2021 13:00:59 -0600 Message-Id: <20211018190115.5365-8-imp@bsdimp.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20211018190115.5365-1-imp@bsdimp.com> References: <20211018190115.5365-1-imp@bsdimp.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: none client-ip=2607:f8b0:4864:20::132; envelope-from=imp@bsdimp.com; helo=mail-il1-x132.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kyle Evans , Richard Henderson , Guy Yur , Laurent Vivier , Warner Losh Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Switch checks for !(flags & MAP_ANONYMOUS) with checks for fd != -1. MAP_STACK and MAP_GUARD both require fd == -1 and don't require mapping the fd either. Add analysis from Guy Yur detailing the different cases for MAP_GUARD and MAP_STACK. Signed-off-by: Guy Yur [ partially merged before, finishing the job and documenting origin] Signed-off-by: Warner Losh Reviewed-by: Richard Henderson Reviewed-by: Kyle Evans --- bsd-user/mmap.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c index face98573f..4ecd949a10 100644 --- a/bsd-user/mmap.c +++ b/bsd-user/mmap.c @@ -127,7 +127,27 @@ error: return ret; } -/* map an incomplete host page */ +/* + * map an incomplete host page + * + * mmap_frag can be called with a valid fd, if flags doesn't contain one of + * MAP_ANON, MAP_STACK, MAP_GUARD. If we need to map a page in those cases, we + * pass fd == -1. However, if flags contains MAP_GUARD then MAP_ANON cannot be + * added. + * + * * If fd is valid (not -1) we want to map the pages with MAP_ANON. + * * If flags contains MAP_GUARD we don't want to add MAP_ANON because it + * will be rejected. See kern_mmap's enforcing of constraints for MAP_GUARD + * in sys/vm/vm_mmap.c. + * * If flags contains MAP_ANON it doesn't matter if we add it or not. + * * If flags contains MAP_STACK, mmap adds MAP_ANON when called so doesn't + * matter if we add it or not either. See enforcing of constraints for + * MAP_STACK in kern_mmap. + * + * Don't add MAP_ANON for the flags that use fd == -1 without specifying the + * flags directly, with the assumption that future flags that require fd == -1 + * will also not require MAP_ANON. + */ static int mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong end, int prot, int flags, int fd, abi_ulong offset) @@ -147,9 +167,9 @@ static int mmap_frag(abi_ulong real_start, } if (prot1 == 0) { - /* no page was there, so we allocate one */ + /* no page was there, so we allocate one. See also above. */ void *p = mmap(host_start, qemu_host_page_size, prot, - flags | MAP_ANON, -1, 0); + flags | ((fd != -1) ? MAP_ANON : 0), -1, 0); if (p == MAP_FAILED) return -1; prot1 = prot; @@ -157,7 +177,7 @@ static int mmap_frag(abi_ulong real_start, prot1 &= PAGE_BITS; prot_new = prot | prot1; - if (!(flags & MAP_ANON)) { + if (fd != -1) { /* msync() won't work here, so we return an error if write is possible while it is a shared mapping */ if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED && @@ -565,7 +585,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot, * worst case: we cannot map the file because the offset is not * aligned, so we read it */ - if (!(flags & MAP_ANON) && + if (fd != -1 && (offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) { /* * msync() won't work here, so we return an error if write is -- 2.32.0