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Fix heuristic that discards segments when matching program segments to mappings #978

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Fix heuristic that discards segments when matching program segments to mappings #978

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a28ad78
Update kernel base to work for non-KASLR kernels.
gmarin13 Oct 17, 2024
0d34dd8
Merge branch 'google:main' into master
gmarin13 Dec 12, 2025
b594114
Fix heuristic that discards segments when matching program segments t…
gmarin13 Dec 13, 2025
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13 changes: 6 additions & 7 deletions internal/elfexec/elfexec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -316,8 +316,7 @@ func ProgramHeadersForMapping(phdrs []elf.ProgHeader, mapOff, mapSz uint64) []*e
// page size is not 4KB, we must try to guess the page size on the system
// where the profile was collected, possibly using the architecture
// specified in the ELF file header.
pageSize = 4096
pageOffsetMask = pageSize - 1
pageSize = 4096
)
mapLimit := mapOff + mapSz
var headers []*elf.ProgHeader
Expand All @@ -331,12 +330,12 @@ func ProgramHeadersForMapping(phdrs []elf.ProgHeader, mapOff, mapSz uint64) []*e
segLimit := p.Off + p.Memsz
// The segment must overlap the mapping.
if p.Type == elf.PT_LOAD && mapOff < segLimit && p.Off < mapLimit {
// If the mapping offset is strictly less than the page aligned segment
// offset, then this mapping comes from a different segment, fixes
// b/179920361.
// If the mapping offset is strictly less than the segment offset aligned
// to the segment p_align value then this mapping comes from a different
// segment, fixes b/179920361.
alignedSegOffset := uint64(0)
if p.Off > (p.Vaddr & pageOffsetMask) {
alignedSegOffset = p.Off - (p.Vaddr & pageOffsetMask)
if p.Off > (p.Vaddr & (p.Align - 1)) {
alignedSegOffset = p.Off - (p.Vaddr & (p.Align - 1))
}
if mapOff < alignedSegOffset {
continue
Expand Down
43 changes: 34 additions & 9 deletions internal/elfexec/elfexec_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -169,13 +169,15 @@ func TestFindProgHeaderForMapping(t *testing.T) {
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0xe10, Vaddr: 0x600e10, Paddr: 0x600e10, Filesz: 0x230, Memsz: 0x238, Align: 0x200000},
}
mediumHeaders := []elf.ProgHeader{
{Type: elf.PT_PHDR, Flags: elf.PF_R, Off: 0x40, Vaddr: 0x40, Paddr: 0x40, Filesz: 0x268, Memsz: 0x268, Align: 8},
{Type: elf.PT_INTERP, Flags: elf.PF_R, Off: 0x2a8, Vaddr: 0x2a8, Paddr: 0x2a8, Filesz: 0x28, Memsz: 0x28, Align: 1},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0, Vaddr: 0, Paddr: 0, Filesz: 0x51800, Memsz: 0x51800, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x51800, Vaddr: 0x251800, Paddr: 0x251800, Filesz: 0x24a8, Memsz: 0x24e8, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x53d00, Vaddr: 0x453d00, Paddr: 0x453d00, Filesz: 0x13a58, Memsz: 0x91a198, Align: 0x200000},
{Type: elf.PT_TLS, Flags: elf.PF_R, Off: 0x51800, Vaddr: 0x51800, Paddr: 0x51800, Filesz: 0x0, Memsz: 0x38, Align: 0x8},
{Type: elf.PT_DYNAMIC, Flags: elf.PF_R | elf.PF_W, Off: 0x51d00, Vaddr: 0x251d00, Paddr: 0x251d00, Filesz: 0x1ef0, Memsz: 0x1ef0, Align: 8},
{Type: elf.PT_PHDR, Flags: elf.PF_R, Off: 0x40, Vaddr: 0x40, Paddr: 0x40, Filesz: 0x2d8, Memsz: 0x2d8, Align: 8},
{Type: elf.PT_INTERP, Flags: elf.PF_R, Off: 0x318, Vaddr: 0x318, Paddr: 0x318, Filesz: 0x28, Memsz: 0x28, Align: 1},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0, Vaddr: 0, Paddr: 0, Filesz: 0x354ca0, Memsz: 0x354ca0, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x400000, Vaddr: 600000, Paddr: 600000, Filesz: 0x0083b8, Memsz: 0x009000, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x600000, Vaddr: 0xa00000, Paddr: 0xa00000, Filesz: 0x007030, Memsz: 0x9cf090, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R, Off: 0x7cf090, Vaddr: 0x15cf090, Paddr: 0x15cf090, Filesz: 0x028460, Memsz: 0x028460, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x7f7500, Vaddr: 0x17f7500, Paddr: 0x17f7500, Filesz: 0x001f80, Memsz: 0x5bdd9a0, Align: 0x200000},
{Type: elf.PT_TLS, Flags: elf.PF_R, Off: 0x407740, Vaddr: 0x607740, Paddr: 0x607740, Filesz: 0x98, Memsz: 0x350, Align: 0x40},
{Type: elf.PT_DYNAMIC, Flags: elf.PF_R | elf.PF_W, Off: 0x407920, Vaddr: 0x607920, Paddr: 0x607920, Filesz: 0x230, Memsz: 0x230, Align: 8},
}
largeHeaders := []elf.ProgHeader{
{Type: elf.PT_PHDR, Flags: elf.PF_R, Off: 0x40, Vaddr: 0x40, Paddr: 0x40, Filesz: 0x268, Memsz: 0x268, Align: 8},
Expand All @@ -186,6 +188,19 @@ func TestFindProgHeaderForMapping(t *testing.T) {
{Type: elf.PT_TLS, Flags: elf.PF_R, Off: 0x2ec5d2c0, Vaddr: 0x2ee5d2c0, Paddr: 0x2ee5d2c0, Filesz: 0x120, Memsz: 0x103f8, Align: 0x40},
{Type: elf.PT_DYNAMIC, Flags: elf.PF_R | elf.PF_W, Off: 0x2ffbc9e0, Vaddr: 0x301bc9e0, Paddr: 0x301bc9e0, Filesz: 0x1f0, Memsz: 0x1f0, Align: 8},
}
largeHeadersWithRoSegment := []elf.ProgHeader{
{Type: elf.PT_PHDR, Flags: elf.PF_R, Off: 0x40, Vaddr: 0x40, Paddr: 0x40, Filesz: 0x348, Memsz: 0x348, Align: 8},
{Type: elf.PT_INTERP, Flags: elf.PF_R, Off: 0x388, Vaddr: 0x388, Paddr: 0x388, Filesz: 0x28, Memsz: 0x28, Align: 1},
{Type: elf.PT_LOAD, Flags: elf.PF_R, Off: 0, Vaddr: 0, Paddr: 0, Filesz: 0x81c5628, Memsz: 0x81c5628, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x81c6000, Vaddr: 0x83c6000, Paddr: 0x83c6000, Filesz: 0x1af7fb0, Memsz: 0x1af7fb0, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0x9cbdfc0, Vaddr: 0xa0bdfc0, Paddr: 0xa0bdfc0, Filesz: 0x16e68fc0, Memsz: 0x16e68fc0, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x20c00000, Vaddr: 0x21200000, Paddr: 0x21200000, Filesz: 0x1c602f8, Memsz: 0x1c61000, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x22a00000, Vaddr: 0x23200000, Paddr: 0x23200000, Filesz: 0x120ed30, Memsz: 0x1d2c2e0, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R, Off: 0x23d2c2e0, Vaddr: 0x2512c2e0, Paddr: 0x2512c2e0, Filesz: 0x2cbc4dc, Memsz: 0x2cbc4dc, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x269e87c0, Vaddr: 0x27fe87c0, Paddr: 0x27fe87c0, Filesz: 0x6f43c8, Memsz: 0x736e00, Align: 0x200000},
{Type: elf.PT_TLS, Flags: elf.PF_R, Off: 0x22840200, Vaddr: 0x22e40200, Paddr: 0x22e40200, Filesz: 0x298, Memsz: 0x5428, Align: 0x40},
{Type: elf.PT_DYNAMIC, Flags: elf.PF_R | elf.PF_W, Off: 0x2285daa0, Vaddr: 0x22e5daa0, Paddr: 0x22e5daa0, Filesz: 0x250, Memsz: 0x250, Align: 8},
}
ffmpegHeaders := []elf.ProgHeader{
{Type: elf.PT_PHDR, Flags: elf.PF_R, Off: 0x40, Vaddr: 0x200040, Paddr: 0x200040, Filesz: 0x1f8, Memsz: 0x1f8, Align: 8},
{Type: elf.PT_INTERP, Flags: elf.PF_R, Off: 0x238, Vaddr: 0x200238, Paddr: 0x200238, Filesz: 0x28, Memsz: 0x28, Align: 1},
Expand Down Expand Up @@ -323,8 +338,8 @@ func TestFindProgHeaderForMapping(t *testing.T) {
desc: "medium file large mapping that includes all address space matches executable segment, b/179920361",
phdrs: mediumHeaders,
pgoff: 0,
memsz: 0xd6e000,
wantHeaders: []*elf.ProgHeader{{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0, Vaddr: 0, Paddr: 0, Filesz: 0x51800, Memsz: 0x51800, Align: 0x200000}},
memsz: 0x73d5000,
wantHeaders: []*elf.ProgHeader{{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0, Vaddr: 0, Paddr: 0, Filesz: 0x354ca0, Memsz: 0x354ca0, Align: 0x200000}},
},
{
desc: "large file executable mapping matches executable segment",
Expand All @@ -347,6 +362,16 @@ func TestFindProgHeaderForMapping(t *testing.T) {
memsz: 0xb11000,
wantHeaders: []*elf.ProgHeader{{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x2ffbe440, Vaddr: 0x303be440, Paddr: 0x303be440, Filesz: 0x4637c0, Memsz: 0xc91610, Align: 0x200000}},
},
{
desc: "large file with RO segment executable mapping includes executable segment",
phdrs: largeHeadersWithRoSegment,
pgoff: 0x9c00000,
memsz: 0x16f27000,
wantHeaders: []*elf.ProgHeader{
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_W, Off: 0x81c6000, Vaddr: 0x83c6000, Paddr: 0x83c6000, Filesz: 0x1af7fb0, Memsz: 0x1af7fb0, Align: 0x200000},
{Type: elf.PT_LOAD, Flags: elf.PF_R | elf.PF_X, Off: 0x9cbdfc0, Vaddr: 0xa0bdfc0, Paddr: 0xa0bdfc0, Filesz: 0x16e68fc0, Memsz: 0x16e68fc0, Align: 0x200000},
},
},
{
desc: "sentry headers, mapping for last page of executable segment matches executable segment",
phdrs: sentryHeaders,
Expand Down