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SubjectRe: [PATCH] x86/mm/pti: Move user W+X check into pti_finalize()
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On Wed, 2018-08-08 at 13:16 +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> The user page-table gets the updated kernel mappings in
> pti_finalize(), which runs after the RO+X permissions got
> applied to the kernel page-table in mark_readonly().
>
> But with CONFIG_DEBUG_WX enabled, the user page-table is
> already checked in mark_readonly() for insecure mappings.
> This causes false-positive warnings, because the user
> page-table did not get the updated mappings yet.
>
> Move the W+X check for the user page-table into
> pti_finalize() after it updated all required mappings.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/include/asm/pgtable.h | 7 +++++--
> arch/x86/mm/dump_pagetables.c | 3 +--
> arch/x86/mm/pti.c | 2 ++
> 3 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable.h
> b/arch/x86/include/asm/pgtable.h
> index e39088cb..a1cb333 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -30,11 +30,14 @@ int __init __early_make_pgtable(unsigned long
> address, pmdval_t pmd);
> void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd);
> void ptdump_walk_pgd_level_debugfs(struct seq_file *m, pgd_t *pgd,
> bool user);
> void ptdump_walk_pgd_level_checkwx(void);
> +void ptdump_walk_user_pgd_level_checkwx(void);
>
> #ifdef CONFIG_DEBUG_WX
> -#define debug_checkwx() ptdump_walk_pgd_level_checkwx()
> +#define debug_checkwx() ptdump_walk_pgd_level_checkwx()
> +#define debug_checkwx_user() ptdump_walk_user_pgd_level_checkwx()
> #else
> -#define debug_checkwx() do { } while (0)
> +#define debug_checkwx() do { } while (0)
> +#define debug_checkwx_user() do { } while (0)
> #endif
>
> /*
> diff --git a/arch/x86/mm/dump_pagetables.c
> b/arch/x86/mm/dump_pagetables.c
> index ccd92c4..b8ab901 100644
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -569,7 +569,7 @@ void ptdump_walk_pgd_level_debugfs(struct seq_file
> *m, pgd_t *pgd, bool user)
> }
> EXPORT_SYMBOL_GPL(ptdump_walk_pgd_level_debugfs);
>
> -static void ptdump_walk_user_pgd_level_checkwx(void)
> +void ptdump_walk_user_pgd_level_checkwx(void)
> {
> #ifdef CONFIG_PAGE_TABLE_ISOLATION
> pgd_t *pgd = INIT_PGD;
> @@ -586,7 +586,6 @@ static void
> ptdump_walk_user_pgd_level_checkwx(void)
> void ptdump_walk_pgd_level_checkwx(void)
> {
> ptdump_walk_pgd_level_core(NULL, NULL, true, false);
> - ptdump_walk_user_pgd_level_checkwx();
> }
>
> static int __init pt_dump_init(void)
> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> index 69a9d60..026a89a 100644
> --- a/arch/x86/mm/pti.c
> +++ b/arch/x86/mm/pti.c
> @@ -628,4 +628,6 @@ void pti_finalize(void)
> */
> pti_clone_entry_text();
> pti_clone_kernel_text();
> +
> + debug_checkwx_user();
> }

I've tested this in a VM and on an Atom laptop, as usual. No
regressions noted.

(The version I tested was the latter pulled into tip:
[ tglx: Folded !NX supported fix ])

Tested-by: David H. Gutteridge <dhgutteridge@sympatico.ca>

Regards,

Dave


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