[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20181008202209.GA6597@zn.tnic>
Date: Mon, 8 Oct 2018 22:22:09 +0200
From: Borislav Petkov <bp@...en8.de>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-tip-commits@...r.kernel.org, luto@...nel.org,
linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
akpm@...ux-foundation.org, tglx@...utronix.de,
dave.hansen@...ux.intel.com, keescook@...omium.org,
jroedel@...e.de, peterz@...radead.org, mingo@...nel.org,
arnd@...db.de, toshi.kani@....com, hpa@...or.com
Subject: Re: [tip:x86/urgent] x86/mm: Avoid VLA in pgd_alloc()
On Fri, Oct 05, 2018 at 09:24:53AM -0700, tip-bot for Arnd Bergmann wrote:
> Commit-ID: 1be3f247c2882a82279cbcf43717581ea943b692
> Gitweb: https://git.kernel.org/tip/1be3f247c2882a82279cbcf43717581ea943b692
> Author: Arnd Bergmann <arnd@...db.de>
> AuthorDate: Fri, 5 Oct 2018 18:13:16 +0200
> Committer: Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 5 Oct 2018 18:16:55 +0200
>
> x86/mm: Avoid VLA in pgd_alloc()
>
> Turning on -Wvla found a new VLA usage:
>
> arch/x86/mm/pgtable.c: In function 'pgd_alloc':
> include/linux/build_bug.h:29:45: error: ISO C90 forbids variable length array 'u_pmds' [-Werror=vla]
> arch/x86/mm/pgtable.c:190:34: note: in expansion of macro 'static_cpu_has'
> #define PREALLOCATED_USER_PMDS (static_cpu_has(X86_FEATURE_PTI) ? \
> ^~~~~~~~~~~~~~
> arch/x86/mm/pgtable.c:431:16: note: in expansion of macro 'PREALLOCATED_USER_PMDS'
> pmd_t *u_pmds[PREALLOCATED_USER_PMDS];
> ^~~~~~~~~~~~~~~~~~~~~~
>
> Use the actual size of the array that is used for X86_FEATURE_PTI
> instead of the variable size.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Toshi Kani <toshi.kani@....com>
> Fixes: 68664695ae57 ("Makefile: Globally enable VLA warning")
> Fixes: f59dbe9ca670 ("x86/pgtable/pae: Use separate kernel PMDs for user page-table")
> Link: http://lkml.kernel.org/r/20181005161333.765973-1-arnd@arndb.de
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
> arch/x86/mm/pgtable.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 089e78c4effd..386b43e3e0ac 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -189,6 +189,7 @@ static void pgd_dtor(pgd_t *pgd)
> */
> #define PREALLOCATED_USER_PMDS (static_cpu_has(X86_FEATURE_PTI) ? \
> KERNEL_PGD_PTRS : 0)
> +#define MAX_PREALLOCATED_USER_PMDS KERNEL_PGD_PTRS
>
> void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
> {
> @@ -211,6 +212,7 @@ void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
> /* No need to prepopulate any pagetable entries in non-PAE modes. */
> #define PREALLOCATED_PMDS 0
> #define PREALLOCATED_USER_PMDS 0
> +#define MAX_PREALLOCATED_USER_PMDS 0
> #endif /* CONFIG_X86_PAE */
>
> static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
> @@ -428,8 +430,8 @@ static inline void _pgd_free(pgd_t *pgd)
> pgd_t *pgd_alloc(struct mm_struct *mm)
> {
> pgd_t *pgd;
> - pmd_t *u_pmds[PREALLOCATED_USER_PMDS];
> - pmd_t *pmds[PREALLOCATED_PMDS];
> + pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
> + pmd_t *pmds[MAX_PREALLOCATED_USER_PMDS];
>
> pgd = _pgd_alloc();
For whatever reason - probably because it forced
MAX_PREALLOCATED_USER_PMDS be KERNEL_PGD_PTRS and not 0 (and I don't
have CONFIG_PAGE_TABLE_ISOLATION so it was 0 here with my .config
before) but this patch causes the fun below.
If I revert it, no splat.
Also, config has CONFIG_X86_PAE=y. And CONFIG_STACKPROTECTOR_STRONG=y. If I
disable _STRONG, it boots too. Attached.
[ 1.749047] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: pgd_alloc+0x29e/0x2a0
[ 1.750306] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 4.19.0-rc6+ #5
[ 1.751353] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014
[ 1.752452] Call Trace:
[ 1.752902] dump_stack+0x66/0x95
[ 1.753426] panic+0x94/0x1dd
[ 1.753922] __stack_chk_fail+0x1e/0x20
[ 1.754486] ? pgd_alloc+0x29e/0x2a0
[ 1.755028] pgd_alloc+0x29e/0x2a0
[ 1.755556] mm_init.isra.60+0x1ec/0x210
[ 1.756128] mm_alloc+0x30/0x40
[ 1.756635] __do_execve_file+0x378/0x930
[ 1.757215] ? __do_execve_file+0x108/0x930
[ 1.757820] ? kmem_cache_alloc+0x123/0x220
[ 1.758414] do_execve+0x2c/0x30
[ 1.758936] run_init_process+0x31/0x36
[ 1.759501] ? rest_init+0xb0/0xb0
[ 1.760029] try_to_run_init_process+0x11/0x33
[ 1.760644] ? rest_init+0xb0/0xb0
[ 1.761173] kernel_init+0x9e/0xda
[ 1.761705] ret_from_fork+0x2e/0x38
[ 1.762309] Kernel Offset: disabled
[ 1.762858] ---[ end Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: pgd_alloc+0x29e/0x2a0 ]---
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
View attachment ".config" of type "text/plain" (103559 bytes)
Powered by blists - more mailing lists