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Mon, 23 Jun 2025 15:00:07 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id cMwkMPdrWWi8cQAAD6G6ig (envelope-from ); Mon, 23 Jun 2025 15:00:07 +0000 From: Vlastimil Babka Date: Mon, 23 Jun 2025 16:59:50 +0200 Subject: [PATCH RFC 1/2] mm, madvise: simplify anon_name handling Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250623-anon_name_cleanup-v1-1-04c94384046f@suse.cz> References: <20250623-anon_name_cleanup-v1-0-04c94384046f@suse.cz> In-Reply-To: <20250623-anon_name_cleanup-v1-0-04c94384046f@suse.cz> To: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , David Hildenbrand , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=5386; i=vbabka@suse.cz; h=from:subject:message-id; bh=4WsgUXbLY0jc0mbRG783m2rvtMBeNkFlZ+M53fOqgQc=; b=owEBbQGS/pANAwAIAbvgsHXSRYiaAcsmYgBoWWvx+Oz6hY4snQoKDFRhXbnRE58Be0Ib+D0Ix Y1TfxhA9yOJATMEAAEIAB0WIQR7u8hBFZkjSJZITfG74LB10kWImgUCaFlr8QAKCRC74LB10kWI mso2CACBbp5TpPZEK987JqU7y7hewVG041bmZcQcTHTMISg3CzJmkx4bR/8VBOHGcmJ6SdycVHG /CyS2Pzjq7ZE5ESEltg5jEsEJgL9ApB61yWTKMhL4gUOuwMDBY7oP1d1Rt29fj/4MIHPeUOACWA ejdSwt380Vw1BTnL+VzvVvTI7BchJzP6K/tbdJic3NYlg8XH+HPx2nKs4zcKk0V9DRvfEb9h8HB 5GNuIG7WmscJyLpg6g69jiUDse+zHfWyBxp3qbu1cfhRs2Zvn0SZR/bbCUOrMeyI6pOgcTnYhVw 1RF23CSkMW9Ckr9jkrfXsEIgTaw1D986nFJ10bIm7sZuGcwd X-Developer-Key: i=vbabka@suse.cz; a=openpgp; fpr=A940D434992C2E8E99103D50224FA7E7CC82A664 X-Spam-Flag: NO X-Spam-Score: -8.30 X-Spamd-Result: default: False [-8.30 / 50.00]; REPLY(-4.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:mid,suse.cz:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Level: Since the introduction in 9a10064f5625 ("mm: add a field to store names for private anonymous memory") the code to set anon_name on a vma has been using madvise_update_vma() to call replace_vma_anon_name(). Since the former is called also by a number of other madvise behaviours that do not set a new anon_name, they have been passing the existing anon_name of the vma to make replace_vma_anon_name() a no-op. This is rather wasteful as it needs anon_vma_name_eq() to determine the no-op situations, and checks for when replace_vma_anon_name() is allowed (the vma is anon/shmem) duplicate the checks already done earlier in madvise_vma_behavior(). It has also lead to commit 942341dcc574 ("mm: fix use-after-free when anon vma name is used after vma is freed") adding anon_name refcount get/put operations exactly to the cases that actually do not change anon_name - just so the replace_vma_anon_name() can keep safely determining it has nothing to do. The recent madvise cleanups made this suboptimal handling very obvious, but happily also allow for an easy fix. madvise_update_vma() now has the complete information whether it's been called to set a new anon_name, so stop passing it the existing vma's name and doing the refcount get/put in its only caller madvise_vma_behavior(). In madvise_update_vma() itself, limit calling of replace_anon_vma_name() only to cases where we are setting a new name, otherwise we know it's a no-op. We can rely solely on the __MADV_SET_ANON_VMA_NAME behaviour and can remove the duplicate checks for vma being anon/shmem that were done already in madvise_vma_behavior(). The remaining reason to obtain the vma's existing anon_name is to pass it to vma_modify_flags_name() for the splitting and merging to work properly. In case of merging, the vma might be freed along with the anon_name, but madvise_update_vma() will not access it afterwards so the UAF previously fixed by commit 942341dcc574 is not reintroduced. Signed-off-by: Vlastimil Babka Reviewed-by: Suren Baghdasaryan --- mm/madvise.c | 37 +++++++++++++------------------------ 1 file changed, 13 insertions(+), 24 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 4491bf080f55d6d1aeffb2ff0b8fdd28904af950..ae29395b4fc7f65a449c5772b19= 01a90f4195885 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -176,21 +176,25 @@ static int replace_anon_vma_name(struct vm_area_struc= t *vma, } #endif /* CONFIG_ANON_VMA_NAME */ /* - * Update the vm_flags on region of a vma, splitting it or merging it as - * necessary. Must be called with mmap_lock held for writing; - * Caller should ensure anon_name stability by raising its refcount even w= hen - * anon_name belongs to a valid vma because this function might free that = vma. + * Update the vm_flags and/or anon_name on region of a vma, splitting it or + * merging it as necessary. Must be called with mmap_lock held for writing. */ static int madvise_update_vma(vm_flags_t new_flags, struct madvise_behavior *madv_behavior) { - int error; struct vm_area_struct *vma =3D madv_behavior->vma; struct madvise_behavior_range *range =3D &madv_behavior->range; - struct anon_vma_name *anon_name =3D madv_behavior->anon_name; + bool set_new_anon_name =3D madv_behavior->behavior =3D=3D __MADV_SET_ANON= _VMA_NAME; + struct anon_vma_name *anon_name; VMA_ITERATOR(vmi, madv_behavior->mm, range->start); =20 - if (new_flags =3D=3D vma->vm_flags && anon_vma_name_eq(anon_vma_name(vma)= , anon_name)) + if (set_new_anon_name) + anon_name =3D madv_behavior->anon_name; + else + anon_name =3D anon_vma_name(vma); + + if (new_flags =3D=3D vma->vm_flags && (!set_new_anon_name + || anon_vma_name_eq(anon_vma_name(vma), anon_name))) return 0; =20 vma =3D vma_modify_flags_name(&vmi, madv_behavior->prev, vma, @@ -203,11 +207,8 @@ static int madvise_update_vma(vm_flags_t new_flags, /* vm_flags is protected by the mmap_lock held in write mode. */ vma_start_write(vma); vm_flags_reset(vma, new_flags); - if (!vma->vm_file || vma_is_anon_shmem(vma)) { - error =3D replace_anon_vma_name(vma, anon_name); - if (error) - return error; - } + if (set_new_anon_name) + return replace_anon_vma_name(vma, anon_name); =20 return 0; } @@ -1313,7 +1314,6 @@ static int madvise_vma_behavior(struct madvise_behavi= or *madv_behavior) int behavior =3D madv_behavior->behavior; struct vm_area_struct *vma =3D madv_behavior->vma; vm_flags_t new_flags =3D vma->vm_flags; - bool set_new_anon_name =3D behavior =3D=3D __MADV_SET_ANON_VMA_NAME; struct madvise_behavior_range *range =3D &madv_behavior->range; int error; =20 @@ -1403,18 +1403,7 @@ static int madvise_vma_behavior(struct madvise_behav= ior *madv_behavior) /* This is a write operation.*/ VM_WARN_ON_ONCE(madv_behavior->lock_mode !=3D MADVISE_MMAP_WRITE_LOCK); =20 - /* - * madvise_update_vma() might cause a VMA merge which could put an - * anon_vma_name, so we must hold an additional reference on the - * anon_vma_name so it doesn't disappear from under us. - */ - if (!set_new_anon_name) { - madv_behavior->anon_name =3D anon_vma_name(vma); 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Mon, 23 Jun 2025 15:00:07 +0000 From: Vlastimil Babka Date: Mon, 23 Jun 2025 16:59:51 +0200 Subject: [PATCH RFC 2/2] mm, madvise: move prctl_set_vma() to mm/madvise.c Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250623-anon_name_cleanup-v1-2-04c94384046f@suse.cz> References: <20250623-anon_name_cleanup-v1-0-04c94384046f@suse.cz> In-Reply-To: <20250623-anon_name_cleanup-v1-0-04c94384046f@suse.cz> To: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , David Hildenbrand , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=6289; i=vbabka@suse.cz; h=from:subject:message-id; bh=GgJ5kuwAujTWdPeQXdF9NpyEneY/99+HBlR3VaCg5ms=; b=owEBbQGS/pANAwAIAbvgsHXSRYiaAcsmYgBoWWv1X4uIKLtSIYHzYzzLjhrnC6u70kUE6f2g/ lcYXseHi62JATMEAAEIAB0WIQR7u8hBFZkjSJZITfG74LB10kWImgUCaFlr9QAKCRC74LB10kWI mvEACACVfDRHAB8UmKGXxmGoefFUbulsxeXJ+OuGoIL5echXIcfuJ8Edpbt9B0/E0/H0TsEj8ym CrqxdoEtbjqf0kaGm0aeo/HUMYTta5pPqahyv8ihouVWBJGcq/Ehxrr90O1TuGJslrqGPthoDYl 2vvVgEsaGGKVYhD4ftF+vQMyo3DHvB/ng+1FvECw3WD3E0qH9e40JlDMncR+Too20VsHsqeSL7b WpCdHexp2rLiCB9wLIAcqZV8t8Sqt/6txea4CaVWM0OzRBB3yTYS7B6j4HdFy5wpKRW0AuL0Kiw wLC/J/1VN2RlhBT4Vx+fl8Z031UiGMMGsUNXSDN3vFxi9DPq X-Developer-Key: i=vbabka@suse.cz; a=openpgp; fpr=A940D434992C2E8E99103D50224FA7E7CC82A664 X-Spamd-Result: default: False [-8.30 / 50.00]; REPLY(-4.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RL7wgbib1ih6q11z93xiyrfhpt)]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.cz:email,suse.cz:mid] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -8.30 Setting anon_name is done via madvise_set_anon_name() and behaves a lot of like other madvise operations. However, apparently because madvise() has lacked the 4th argument and prctl() not, the userspace entry point has been implemented via prctl(PR_SET_VMA, ...) and handled first by prctl_set_vma(). Currently prctl_set_vma() lives in kernel/sys.c but it's mm code so move it under mm. mm/madvise.c seems to be the most straightforward place as that's where madvise_set_anon_name() lives, so we can stop declaring the latter in the header and instead declare prctl_set_vma(). It's not ideal as prctl is not madvise, but that's the reality we live in, as described above. Signed-off-by: Vlastimil Babka --- include/linux/mm.h | 13 +++++------ kernel/sys.c | 64 --------------------------------------------------= ---- mm/madvise.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 63 insertions(+), 73 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 0e0549f3d681f6c7a78e8dfa341a810e5a8f96c1..1f8c2561c8cf77e9bb695094325= 401c09c15f3e6 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -4059,14 +4059,13 @@ unsigned long wp_shared_mapping_range(struct addres= s_space *mapping, #endif =20 #ifdef CONFIG_ANON_VMA_NAME -int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, - unsigned long len_in, - struct anon_vma_name *anon_name); +int prctl_set_vma(unsigned long opt, unsigned long start, + unsigned long size, unsigned long arg); #else -static inline int -madvise_set_anon_name(struct mm_struct *mm, unsigned long start, - unsigned long len_in, struct anon_vma_name *anon_name) { - return 0; +static inline int prctl_set_vma(unsigned long opt, unsigned long start, + unsigned long size, unsigned long arg) +{ + return -EINVAL; } #endif =20 diff --git a/kernel/sys.c b/kernel/sys.c index adc0de0aa364aebb23999f621717a5d32599921c..247d8925daa6fc8613450404283= 2c2164b5d8277 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2343,70 +2343,6 @@ int __weak arch_lock_shadow_stack_status(struct task= _struct *t, unsigned long st =20 #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE) =20 -#ifdef CONFIG_ANON_VMA_NAME - -#define ANON_VMA_NAME_MAX_LEN 80 -#define ANON_VMA_NAME_INVALID_CHARS "\\`$[]" - -static inline bool is_valid_name_char(char ch) -{ - /* printable ascii characters, excluding ANON_VMA_NAME_INVALID_CHARS */ - return ch > 0x1f && ch < 0x7f && - !strchr(ANON_VMA_NAME_INVALID_CHARS, ch); -} - -static int prctl_set_vma(unsigned long opt, unsigned long addr, - unsigned long size, unsigned long arg) -{ - struct mm_struct *mm =3D current->mm; - const char __user *uname; - struct anon_vma_name *anon_name =3D NULL; - int error; - - switch (opt) { - case PR_SET_VMA_ANON_NAME: - uname =3D (const char __user *)arg; - if (uname) { - char *name, *pch; - - name =3D strndup_user(uname, ANON_VMA_NAME_MAX_LEN); - if (IS_ERR(name)) - return PTR_ERR(name); - - for (pch =3D name; *pch !=3D '\0'; pch++) { - if (!is_valid_name_char(*pch)) { - kfree(name); - return -EINVAL; - } - } - /* anon_vma has its own copy */ - anon_name =3D anon_vma_name_alloc(name); - kfree(name); - if (!anon_name) - return -ENOMEM; - - } - - mmap_write_lock(mm); - error =3D madvise_set_anon_name(mm, addr, size, anon_name); - mmap_write_unlock(mm); - anon_vma_name_put(anon_name); - break; - default: - error =3D -EINVAL; - } - - return error; -} - -#else /* CONFIG_ANON_VMA_NAME */ -static int prctl_set_vma(unsigned long opt, unsigned long start, - unsigned long size, unsigned long arg) -{ - return -EINVAL; -} -#endif /* CONFIG_ANON_VMA_NAME */ - static inline unsigned long get_current_mdwe(void) { unsigned long ret =3D 0; diff --git a/mm/madvise.c b/mm/madvise.c index ae29395b4fc7f65a449c5772b1901a90f4195885..4a8e61e2c5025726bc2ce1f3237= 68c5b25cef2c9 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -31,6 +31,7 @@ #include #include #include +#include =20 #include =20 @@ -134,8 +135,8 @@ static int replace_anon_vma_name(struct vm_area_struct = *vma, return 0; } =20 -int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, - unsigned long len_in, struct anon_vma_name *anon_name) +static int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, + unsigned long len_in, struct anon_vma_name *anon_name) { unsigned long end; unsigned long len; @@ -165,6 +166,60 @@ int madvise_set_anon_name(struct mm_struct *mm, unsign= ed long start, madv_behavior.range.end =3D end; return madvise_walk_vmas(&madv_behavior); } + +#define ANON_VMA_NAME_MAX_LEN 80 +#define ANON_VMA_NAME_INVALID_CHARS "\\`$[]" + +static inline bool is_valid_name_char(char ch) +{ + /* printable ascii characters, excluding ANON_VMA_NAME_INVALID_CHARS */ + return ch > 0x1f && ch < 0x7f && + !strchr(ANON_VMA_NAME_INVALID_CHARS, ch); +} + +int prctl_set_vma(unsigned long opt, unsigned long addr, + unsigned long size, unsigned long arg) +{ + struct mm_struct *mm =3D current->mm; + const char __user *uname; + struct anon_vma_name *anon_name =3D NULL; + int error; + + switch (opt) { + case PR_SET_VMA_ANON_NAME: + uname =3D (const char __user *)arg; + if (uname) { + char *name, *pch; + + name =3D strndup_user(uname, ANON_VMA_NAME_MAX_LEN); + if (IS_ERR(name)) + return PTR_ERR(name); + + for (pch =3D name; *pch !=3D '\0'; pch++) { + if (!is_valid_name_char(*pch)) { + kfree(name); + return -EINVAL; + } + } + /* anon_vma has its own copy */ + anon_name =3D anon_vma_name_alloc(name); + kfree(name); + if (!anon_name) + return -ENOMEM; + + } + + mmap_write_lock(mm); + error =3D madvise_set_anon_name(mm, addr, size, anon_name); + mmap_write_unlock(mm); + anon_vma_name_put(anon_name); + break; + default: + error =3D -EINVAL; + } + + return error; +} #else /* CONFIG_ANON_VMA_NAME */ static int replace_anon_vma_name(struct vm_area_struct *vma, struct anon_vma_name *anon_name) --=20 2.50.0