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author | Gustavo A. R. Silva <gustavoars@kernel.org> | 2022-09-21 21:46:03 +0300 |
---|---|---|
committer | Kees Cook <keescook@chromium.org> | 2022-12-01 19:50:38 +0300 |
commit | 25226df4b9be7f6d5d722af5b75e86e76e5c3a80 (patch) | |
tree | b239c4023a2c2aa10b1b0c7750563c7deee3c665 /arch | |
parent | 38931d8989b5760b0bd17c9ec99e81986258e4cb (diff) | |
download | linux-25226df4b9be7f6d5d722af5b75e86e76e5c3a80.tar.xz |
mm/pgtable: Fix multiple -Wstringop-overflow warnings
The actual size of the following arrays at run-time depends on
CONFIG_X86_PAE.
427 pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
428 pmd_t *pmds[MAX_PREALLOCATED_PMDS];
If CONFIG_X86_PAE is not enabled, their final size will be zero (which
is technically not a legal storage size in C, but remains "valid" via
the GNU extension). In that case, the compiler complains about trying to
access objects of size zero when calling functions where these objects
are passed as arguments.
Fix this by sanity-checking the size of those arrays just before the
function calls. Also, the following warnings are fixed by these changes
when building with GCC 11+ and -Wstringop-overflow enabled:
arch/x86/mm/pgtable.c:437:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
arch/x86/mm/pgtable.c:440:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
arch/x86/mm/pgtable.c:462:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
arch/x86/mm/pgtable.c:455:9: warning: ‘pgd_prepopulate_user_pmd’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
arch/x86/mm/pgtable.c:464:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
This is one of the last cases in the ongoing effort to globally enable
-Wstringop-overflow.
The alternative to this is to make the originally suggested change:
make the pmds argument from an array pointer to a pointer pointer. That
situation is considered "legal" for C in the sense that it does not have
a way to reason about the storage. i.e.:
-static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[])
+static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t **pmds)
With the above change, there's no difference in binary output, and the
compiler warning is silenced.
However, with this patch, the compiler can actually figure out that it
isn't using the code at all, and it gets dropped:
text data bss dec hex filename
8218 718 32 8968 2308 arch/x86/mm/pgtable.o.before
7765 694 32 8491 212b arch/x86/mm/pgtable.o.after
So this case (fixing a warning and reducing image size) is a clear win.
Additionally drops an old work-around for GCC in the same code.
Link: https://github.com/KSPP/linux/issues/203
Link: https://github.com/KSPP/linux/issues/181
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/Yytb67xvrnctxnEe@work
Diffstat (limited to 'arch')
-rw-r--r-- | arch/x86/mm/pgtable.c | 22 |
1 files changed, 13 insertions, 9 deletions
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 8525f2876fb4..e4f499eb0f29 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -299,9 +299,6 @@ static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[]) pud_t *pud; int i; - if (PREALLOCATED_PMDS == 0) /* Work around gcc-3.4.x bug */ - return; - p4d = p4d_offset(pgd, 0); pud = pud_offset(p4d, 0); @@ -434,10 +431,12 @@ pgd_t *pgd_alloc(struct mm_struct *mm) mm->pgd = pgd; - if (preallocate_pmds(mm, pmds, PREALLOCATED_PMDS) != 0) + if (sizeof(pmds) != 0 && + preallocate_pmds(mm, pmds, PREALLOCATED_PMDS) != 0) goto out_free_pgd; - if (preallocate_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS) != 0) + if (sizeof(u_pmds) != 0 && + preallocate_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS) != 0) goto out_free_pmds; if (paravirt_pgd_alloc(mm) != 0) @@ -451,17 +450,22 @@ pgd_t *pgd_alloc(struct mm_struct *mm) spin_lock(&pgd_lock); pgd_ctor(mm, pgd); - pgd_prepopulate_pmd(mm, pgd, pmds); - pgd_prepopulate_user_pmd(mm, pgd, u_pmds); + if (sizeof(pmds) != 0) + pgd_prepopulate_pmd(mm, pgd, pmds); + + if (sizeof(u_pmds) != 0) + pgd_prepopulate_user_pmd(mm, pgd, u_pmds); spin_unlock(&pgd_lock); return pgd; out_free_user_pmds: - free_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS); + if (sizeof(u_pmds) != 0) + free_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS); out_free_pmds: - free_pmds(mm, pmds, PREALLOCATED_PMDS); + if (sizeof(pmds) != 0) + free_pmds(mm, pmds, PREALLOCATED_PMDS); out_free_pgd: _pgd_free(pgd); out: |