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[34.150.132.193]) by smtp.gmail.com with ESMTPSA id u21-20020ae9c015000000b007675c4b530fsm2075957qkk.28.2023.07.22.16.15.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Jul 2023 16:15:14 -0700 (PDT) From: Pasha Tatashin To: pasha.tatashin@soleen.com, akpm@linux-foundation.org, corbet@lwn.net, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rick.p.edgecombe@intel.com Subject: [PATCH v2 1/3] mm/page_table_check: Do WARN_ON instead of BUG_ON Date: Sat, 22 Jul 2023 23:15:06 +0000 Message-ID: <20230722231508.1030269-2-pasha.tatashin@soleen.com> X-Mailer: git-send-email 2.41.0.487.g6d72f3e995-goog In-Reply-To: <20230722231508.1030269-1-pasha.tatashin@soleen.com> References: <20230722231508.1030269-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Currently, page_table_check when detects errors panics the kernel. Instead, print a warning as it is more useful compared to unconditionally crashing the machine. However, once a warning is detected, the counting of page_table_check becomes unbalanced, therefore, disable its activity until the next boot. In case of where machine hardening requires a more secure environment, it is still possible to crash machine on page_table_check errors via panic_on_warn sysctl option. Signed-off-by: Pasha Tatashin --- mm/page_table_check.c | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-) diff --git a/mm/page_table_check.c b/mm/page_table_check.c index 93ec7690a0d8..ad4447e999f8 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -22,6 +22,12 @@ static bool __page_table_check_enabled __initdata =3D DEFINE_STATIC_KEY_TRUE(page_table_check_disabled); EXPORT_SYMBOL(page_table_check_disabled); =20 +#define PAGE_TABLE_CHECK_WARN(v) \ + do { \ + if (WARN_ON_ONCE(v)) \ + static_branch_enable(&page_table_check_disabled); \ + } while (false) + static int __init early_page_table_check_param(char *buf) { return kstrtobool(buf, &__page_table_check_enabled); @@ -50,7 +56,8 @@ struct page_ext_operations page_table_check_ops =3D { =20 static struct page_table_check *get_page_table_check(struct page_ext *page= _ext) { - BUG_ON(!page_ext); + PAGE_TABLE_CHECK_WARN(!page_ext); + return (void *)(page_ext) + page_table_check_ops.offset; } =20 @@ -72,18 +79,18 @@ static void page_table_check_clear(struct mm_struct *mm= , unsigned long addr, page =3D pfn_to_page(pfn); page_ext =3D page_ext_get(page); =20 - BUG_ON(PageSlab(page)); + PAGE_TABLE_CHECK_WARN(PageSlab(page)); anon =3D PageAnon(page); =20 for (i =3D 0; i < pgcnt; i++) { struct page_table_check *ptc =3D get_page_table_check(page_ext); =20 if (anon) { - BUG_ON(atomic_read(&ptc->file_map_count)); - BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->file_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_dec_return(&ptc->anon_map_count) < 0); } else { - BUG_ON(atomic_read(&ptc->anon_map_count)); - BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->anon_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_dec_return(&ptc->file_map_count) < 0); } page_ext =3D page_ext_next(page_ext); } @@ -110,18 +117,18 @@ static void page_table_check_set(struct mm_struct *mm= , unsigned long addr, page =3D pfn_to_page(pfn); page_ext =3D page_ext_get(page); =20 - BUG_ON(PageSlab(page)); + PAGE_TABLE_CHECK_WARN(PageSlab(page)); anon =3D PageAnon(page); =20 for (i =3D 0; i < pgcnt; i++) { struct page_table_check *ptc =3D get_page_table_check(page_ext); =20 if (anon) { - BUG_ON(atomic_read(&ptc->file_map_count)); - BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->file_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_inc_return(&ptc->anon_map_count) > 1 && rw= ); } else { - BUG_ON(atomic_read(&ptc->anon_map_count)); - BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->anon_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_inc_return(&ptc->file_map_count) < 0); } page_ext =3D page_ext_next(page_ext); } @@ -137,15 +144,15 @@ void __page_table_check_zero(struct page *page, unsig= ned int order) struct page_ext *page_ext; unsigned long i; =20 - BUG_ON(PageSlab(page)); + PAGE_TABLE_CHECK_WARN(PageSlab(page)); =20 page_ext =3D page_ext_get(page); - BUG_ON(!page_ext); + PAGE_TABLE_CHECK_WARN(!page_ext); for (i =3D 0; i < (1ul << order); i++) { struct page_table_check *ptc =3D get_page_table_check(page_ext); =20 - BUG_ON(atomic_read(&ptc->anon_map_count)); - BUG_ON(atomic_read(&ptc->file_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->anon_map_count)); + PAGE_TABLE_CHECK_WARN(atomic_read(&ptc->file_map_count)); page_ext =3D page_ext_next(page_ext); } page_ext_put(page_ext); --=20 2.41.0.487.g6d72f3e995-goog