gcov: use atomic counter updates to fix concurrent access crashes
In the Linux kernel, the following vulnerability has been resolved: gcov: use atomic counter updates to fix concurrent access crashes GCC's GCOV instrumentation can merge global branch counters with loop induction variables as an optimization. In inflate_fast(), the inner copy loops get transformed so that the GCOV counter value is loaded multiple times to compute the loop base address, start index, and end bound. Since GCOV counters are global (not per-CPU), concurrent execution on different CPUs causes the counter to change between loads, producing inconsistent values and out-of-bounds memory writes. The crash manifests during IPComp (IP Payload Compression) processing when inflate_fast() runs concurrently on multiple CPUs: BUG: unable to handle page fault for address: ffffd0a3c0902ffa RIP: inflate_fast+1431 Call Trace: zlib_inflate __deflate_decompress crypto_comp_decompress ipcomp_decompress [xfrm_ipcomp] ipcomp_input [xfrm_ipcomp] xfrm_input At the crash point, the compiler generated three loads from the same global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and end for an indexed loop. Another CPU modified the counter between loads, making the values inconsistent - the write went 3.4 MB past a 65 KB buffer. Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in the top-level Makefile, guarded by a try-run compile test. The test compiles a minimal program with and without -fprofile-update=prefer-atomic using the full KBUILD_CFLAGS,
CVE-2026-63825
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-63825
Linux
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Linux
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2521f2c228ad750701ba4702484e31d876dbc386",
"lessThan": "b0f7bd5eeb903a0021a80e9d704814e2a9d3998c",
"versionType": "git"
},
{
"status": "affected",
"version": "2521f2c228ad750701ba4702484e31d876dbc386",
"lessThan": "4575852c23a10abc7648d31e4c12cf79d7391637",
"versionType": "git"
},
{
"status": "affected",
"version": "2521f2c228ad750701ba4702484e31d876dbc386",
"lessThan": "49d893b9cbcfc5802a32e53a64c6c6956670d65b",
"versionType": "git"
},
{
"status": "affected",
"version": "2521f2c228ad750701ba4702484e31d876dbc386",
"lessThan": "5b959c1dbb4522b9e3ac4e26ad638b8784869841",
"versionType": "git"
},
{
"status": "affected",
"version": "2521f2c228ad750701ba4702484e31d876dbc386",
"lessThan": "56cb9b7d96b28a1173a510ab25354b6599ad3a33",
"versionType": "git"
}
],
"programFiles": [
"Makefile"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2.6.31"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "2.6.31",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.6.160",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.114",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.38",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.1.3",
"versionType": "semver",
"lessThanOrEqual": "7.1.*"
},
{
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"Makefile"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-63825
Source reference:
/cveMetadata/cveId
Publisher severity
critical
Source reference: /containers/cna/metrics
- Event
- #46397 · Revision 1
- Added to Heist Feed
- Publisher date