forked from pool/dwarves
94 lines
3.4 KiB
Diff
94 lines
3.4 KiB
Diff
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From 4639af69cb52367f22ac39a51607c7af57ef5029 Mon Sep 17 00:00:00 2001
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From: Alan Maguire <alan.maguire@oracle.com>
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Date: Fri, 21 Oct 2022 16:02:03 +0100
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Subject: [PATCH 7/7] dwarves: Zero-initialize struct cu in cu__new() to
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prevent incorrect BTF types
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BTF deduplication was throwing some strange results, where core kernel
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data types were failing to deduplicate due to the return values
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of function type members being void (0) instead of the actual type
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(unsigned int). An example of this can be seen below, where
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"struct dst_ops" was failing to deduplicate between kernel and
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module:
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struct dst_ops {
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short unsigned int family;
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unsigned int gc_thresh;
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int (*gc)(struct dst_ops *);
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struct dst_entry * (*check)(struct dst_entry *, __u32);
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unsigned int (*default_advmss)(const struct dst_entry *);
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unsigned int (*mtu)(const struct dst_entry *);
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...
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struct dst_ops___2 {
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short unsigned int family;
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unsigned int gc_thresh;
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int (*gc)(struct dst_ops___2 *);
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struct dst_entry___2 * (*check)(struct dst_entry___2 *, __u32);
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void (*default_advmss)(const struct dst_entry___2 *);
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void (*mtu)(const struct dst_entry___2 *);
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...
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This was seen with
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bcc648a10cbc ("btf_encoder: Encode DW_TAG_unspecified_type returning routines as void")
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...which rewrites the return value as 0 (void) when it is marked
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as matching DW_TAG_unspecified_type:
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static int32_t btf_encoder__tag_type(struct btf_encoder *encoder, uint32_t type_id_off, uint32_t tag_type)
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{
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if (tag_type == 0)
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return 0;
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if (encoder->cu->unspecified_type.tag && tag_type == encoder->cu->unspecified_type.type) {
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// No provision for encoding this, turn it into void.
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return 0;
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}
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return type_id_off + tag_type;
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}
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However the odd thing was that on further examination, the unspecified type
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was not being set, so why was this logic being tripped? Futher debugging
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showed that the encoder->cu->unspecified_type.tag value was garbage, and
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the type id happened to collide with "unsigned int"; as a result we
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were replacing unsigned ints with void return values, and since this
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was being done to function type members in structs, it triggered a
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type mismatch which failed deduplication between kernel and module.
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The fix is simply to calloc() the cu in cu__new() instead.
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Committer notes:
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We have zalloc(size) as an alias to calloc(1, size), use it instead.
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Fixes: bcc648a10cbcd0b9 ("btf_encoder: Encode DW_TAG_unspecified_type returning routines as void")
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Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
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Acked-by: Andrii Nakryiko <andrii@kernel.org>
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Acked-by: Jiri Olsa <jolsa@kernel.org>
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Cc: bpf@vger.kernel.org
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Cc: dwarves@vger.kernel.org
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Link: https://lore.kernel.org/r/1666364523-9648-1-git-send-email-alan.maguire@oracle.com
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Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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---
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dwarves.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/dwarves.c b/dwarves.c
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index 32bfec5ea0f1a338..ff449affff94b16f 100644
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--- a/dwarves.c
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+++ b/dwarves.c
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@@ -625,7 +625,7 @@ struct cu *cu__new(const char *name, uint8_t addr_size,
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const unsigned char *build_id, int build_id_len,
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const char *filename, bool use_obstack)
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{
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- struct cu *cu = malloc(sizeof(*cu) + build_id_len);
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+ struct cu *cu = zalloc(sizeof(*cu) + build_id_len);
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if (cu != NULL) {
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uint32_t void_id;
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--
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2.39.1
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