Initialize never-used descriptors as permanently invalid so there is no risk of the descriptor unexpectedly being determined as valid due to dataring head overflowing/wrapping.
Signed-off-by: John Ogness <john.ogn...@linutronix.de> --- kernel/printk/dataring.c | 42 +++++++++++++++++++++++++++----------- kernel/printk/dataring.h | 12 +++++++++++ kernel/printk/ringbuffer.c | 5 +++++ kernel/printk/ringbuffer.h | 7 ++++++- 4 files changed, 53 insertions(+), 13 deletions(-) diff --git a/kernel/printk/dataring.c b/kernel/printk/dataring.c index 6642e085a05d..345c46dba5bb 100644 --- a/kernel/printk/dataring.c +++ b/kernel/printk/dataring.c @@ -316,8 +316,8 @@ static unsigned long _dataring_pop(struct dataring *dr, * If dB reads from gA, then dD reads from fH. * If dB reads from gA, then dE reads from fE. * - * Note that if dB reads from gA, then dC cannot read from fC. - * Note that if dB reads from gA, then dD cannot read from fD. + * Note that if dB reads from gA, then dC cannot read from fC->nA. + * Note that if dB reads from gA, then dD cannot read from fC->nB. * * Relies on: * @@ -489,6 +489,30 @@ static bool get_new_lpos(struct dataring *dr, unsigned int size, } } +/** + * dataring_desc_init() - Initialize a descriptor to be permanently invalid. + * + * @desc: The descriptor to initialize. + * + * Setting a descriptor to be permanently invalid means that there is no risk + * of the descriptor later unexpectedly being determined as valid due to + * overflowing/wrapping of @head_lpos. + */ +void dataring_desc_init(struct dr_desc *desc) +{ + /* + * An unaligned @begin_lpos can never point to a data block and + * having the same value for @begin_lpos and @next_lpos is also + * invalid. + */ + + /* nA: */ + WRITE_ONCE(desc->begin_lpos, 1); + + /* nB: */ + WRITE_ONCE(desc->next_lpos, 1); +} + /** * dataring_push() - Reserve a data block in the data array. * @@ -568,20 +592,14 @@ char *dataring_push(struct dataring *dr, unsigned int size, if (!ret) { /* + * fC: + * * Force @desc permanently invalid to minimize risk * of the descriptor later unexpectedly being * determined as valid due to overflowing/wrapping of - * @head_lpos. An unaligned @begin_lpos can never - * point to a data block and having the same value - * for @begin_lpos and @next_lpos is also invalid. + * @head_lpos. */ - - /* fC: */ - WRITE_ONCE(desc->begin_lpos, 1); - - /* fD: */ - WRITE_ONCE(desc->next_lpos, 1); - + dataring_desc_init(desc); return NULL; } /* fE: */ diff --git a/kernel/printk/dataring.h b/kernel/printk/dataring.h index 346a455a335a..413ee95f4dd6 100644 --- a/kernel/printk/dataring.h +++ b/kernel/printk/dataring.h @@ -43,6 +43,17 @@ struct dr_desc { unsigned long next_lpos; }; +/* + * Initialize a descriptor to be permanently invalid so there is no risk + * of the descriptor later unexpectedly being determined as valid due to + * overflowing/wrapping of @head_lpos. + */ +#define __DR_DESC_INITIALIZER \ + { \ + .begin_lpos = 1, \ + .next_lpos = 1, \ + } + /** * struct dataring - A data ringbuffer with support for entry IDs. * @@ -90,6 +101,7 @@ void dataring_datablock_setid(struct dataring *dr, struct dr_desc *desc, struct dr_datablock *dataring_getdatablock(struct dataring *dr, struct dr_desc *desc, int *size); bool dataring_datablock_isvalid(struct dataring *dr, struct dr_desc *desc); +void dataring_desc_init(struct dr_desc *desc); void dataring_desc_copy(struct dr_desc *dst, struct dr_desc *src); #endif /* _KERNEL_PRINTK_DATARING_H */ diff --git a/kernel/printk/ringbuffer.c b/kernel/printk/ringbuffer.c index b9fc13597b10..9be841761ea2 100644 --- a/kernel/printk/ringbuffer.c +++ b/kernel/printk/ringbuffer.c @@ -345,6 +345,11 @@ static bool assign_desc(struct prb_reserved_entry *e) if (i < DESCS_COUNT(rb)) { d = &rb->descs[i]; atomic_long_set(&d->id, i); + /* + * Initialize the new descriptor such that + * it is permanently invalid. + */ + dataring_desc_init(&d->desc); break; } } diff --git a/kernel/printk/ringbuffer.h b/kernel/printk/ringbuffer.h index 9fe54a09fbc2..462b4d3a3ee2 100644 --- a/kernel/printk/ringbuffer.h +++ b/kernel/printk/ringbuffer.h @@ -178,7 +178,12 @@ struct dr_desc *prb_getdesc(unsigned long id, void *arg); char _##name##_data[(1 << ((avgdatabits) + (descbits))) + \ sizeof(long)] \ __aligned(__alignof__(long)); \ -struct prb_desc _##name##_descs[1 << (descbits)]; \ +struct prb_desc _##name##_descs[1 << (descbits)] = { \ + { \ + .id = ATOMIC_LONG_INIT(0), \ + .desc = __DR_DESC_INITIALIZER, \ + }, \ + }; \ struct printk_ringbuffer name = { \ .desc_count_bits = descbits, \ .descs = &_##name##_descs[0], \ -- 2.20.1