From: Stephen Brennan stephen.s.brennan@oracle.com
mainline inclusion from mainline-v6.11-rc6 commit 04c8abae1b7b2abeb638a3d5d5950fa2a031c244 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IB2BWT CVE: CVE-2024-50102
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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The runtime constant feature removes all the users of these variables, allowing the compiler to optimize them away. It's quite difficult to extract their values from the kernel text, and the memory saved by removing them is tiny, and it was never the point of this optimization.
Since the dentry_hashtable is a core data structure, it's valuable for debugging tools to be able to read it easily. For instance, scripts built on drgn, like the dentrycache script[1], rely on it to be able to perform diagnostics on the contents of the dcache. Annotate it as used, so the compiler doesn't discard it.
Link: https://github.com/oracle-samples/drgn-tools/blob/3afc56146f54d09dfd1f6d3c1b... [1] Fixes: e3c92e81711d ("runtime constants: add x86 architecture support") Signed-off-by: Stephen Brennan stephen.s.brennan@oracle.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
Conflicts: fs/dcache.c [Context conflicts] Signed-off-by: Qi Xi xiqi2@huawei.com --- fs/dcache.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c index 3e0b9abbf4d8..ea0784aff435 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -94,11 +94,16 @@ EXPORT_SYMBOL(dotdot_name); * * This hash-function tries to avoid losing too many bits of hash * information, yet avoid using a prime hash-size or similar. + * + * Marking the variables "used" ensures that the compiler doesn't + * optimize them away completely on architectures with runtime + * constant infrastructure, this allows debuggers to see their + * values. But updating these values has no effect on those arches. */
-static unsigned int d_hash_shift __read_mostly; +static unsigned int d_hash_shift __ro_after_init __used;
-static struct hlist_bl_head *dentry_hashtable __read_mostly; +static struct hlist_bl_head *dentry_hashtable __ro_after_init __used;
static inline struct hlist_bl_head *d_hash(unsigned int hash) {